Patent Publication Number: US-2023165101-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2021-191568, filed on Nov. 25, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     An embodiment of the present invention relates to a display device and a method for manufacturing the same. 
     BACKGROUND 
     Conventionally, an organic EL display device (Organic Electroluminescence Display) using an organic electroluminescent material (organic EL material) as a light-emitting element (organic EL element) of a display unit has been known as a display device. In recent years, there has been an increasing demand for higher definition in an organic EL display device. 
     As the definition of the EL display device is increased, Adjacent pixels become closer together, and therefore, an effect of a leakage current flowing between adjacent pixels (hereinafter, also referred to as “leakage current in the transverse direction”) is actualized. In the EL display device, the leakage current in the transverse direction may cause the adjacent pixels to emit light, thereby deteriorating the quality of the EL display device. For example, see Japanese laid-open patent publication No. 2011-009169. 
     SUMMARY 
     A display device includes a first pixel electrode, a second pixel electrode arranged separately from the first pixel electrode in a first direction, an insulating layer covering the first pixel electrode and the second pixel electrode, the insulating layer including a first opening part and a second opening part, the first opening part exposing at least a part of an upper surface of the first pixel electrode, and the second opening part exposing at least a part of an upper surface of the second pixel electrode, a first light-emitting layer arranged at a position overlapping the first pixel electrode, a second light-emitting layer arranged at a position overlapping the second pixel electrode, and a counter electrode arranged above the first light-emitting layer and the second light-emitting layer, and a light emission start voltage of the second light-emitting layer is lower than a light emission start voltage of the first light-emitting layer, the second light-emitting layer includes a first area arranged at a first end portion adjacent to the first light-emitting layer, the first area having a first dopant concentration, and a second area arranged at a second end portion of the second light-emitting layer opposing to the first end portion, the second area having a second dopant concentration higher than the first dopant concentration. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram when a display device according to an embodiment of the present invention is in a plan view. 
         FIG.  2    is an enlarged view of a pixel layout when a display device is in a plan view. 
         FIG.  3    is a cross-sectional view when a display device shown in  FIG.  2    is cut along a line A 1 -A 2 . 
         FIG.  4    is a partially enlarged view of the cross-sectional view shown in  FIG.  3   . 
         FIG.  5    is a cross-sectional view illustrating a method for manufacturing a light-emitting layer according to an embodiment of the present invention. 
         FIG.  6    is a cross-sectional view illustrating a method for manufacturing a display device according to an embodiment of the present invention. 
         FIG.  7    is a cross-sectional view illustrating a method for manufacturing a display device according to an embodiment of the present invention. 
         FIG.  8    is a cross-sectional view illustrating a method for manufacturing a display device according to an embodiment of the present invention. 
         FIG.  9    is a cross-sectional view illustrating a method for manufacturing a display device according to an embodiment of the present invention. 
         FIG.  10    is a pixel layout diagram when a display device according to an embodiment of the present invention is in a plan view. 
         FIG.  11    is a cross-sectional view when a display device shown in  FIG.  10    is cut along a line A 1 -A 2 . 
         FIG.  12    is an enlarged view of a pixel layout when a conventional display device is in a plan view. 
         FIG.  13    is a cross-sectional view when a display area shown in  FIG.  12    is cut along a line F 1 -F 2 . 
         FIG.  14    is a partially enlarged view of the cross-sectional view shown in  FIG.  13   . 
         FIG.  15    is a cross-sectional view when a display area shown in  FIG.  15    is cut along a line F 1 -F 2 . 
         FIG.  16    is a partially enlarged view of the cross-sectional view shown in  FIG.  15   . 
         FIG.  17    is a cross-sectional view illustrating a method for manufacturing a conventional light-emitting layer. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention provides a display device in which a leakage current in a transverse direction in a light-emitting element is suppressed. 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. However, the present invention can be implemented in various aspects without departing from the gist thereof and is not to be construed as being limited to the description of the embodiments exemplified below. In addition, in order to make the description clearer with respect to the drawings, the width, thickness, shape, and the like of each part may be schematically represented in comparison with actual embodiments, but the schematic drawings are merely examples, and do not limit the interpretation of the present invention. Further, in this specification and the drawings, the same or similar elements as those described with respect to the above-described drawings are indicated by the same symbols, and a redundant description may be omitted. 
     In the present invention, when a single film is processed to form a plurality of films, the plurality of films may have different functions and roles. However, the plurality of films derive from films formed as the same layer in the same process, and they have the same layer structure and the same material. Therefore, the plurality of films is defined as existing in the same layer. 
     Also, in this specification, expressions such as “upper” and “lower” in describing the drawings represent relative positional relationships between a structure of interest and other structures. In this specification, in a side view, the direction from an insulating surface to a light-emitting element, which will be described later, is defined as “upper”, and a reverse direction thereof is defined as “lower”. In this specification and the claims, the expression “on” in describing the manner of arranging another structure on a certain structure shall include both arranging another structure directly above a certain structure and arranging another structure above a certain structure via yet another structure, unless otherwise specified. 
     A display device according to an embodiment of the present invention will be described referring to  FIG.  1    to  FIG.  9   .  FIG.  1    is a schematic diagram showing a configuration of a display device  100  according to an embodiment of the present invention and shows a schematic configuration when the display device  100  is in a plan view. In this specification, a state in which the display device  100  is viewed perpendicularly to a screen (display area) is referred to as a “plan view.” 
     As shown in  FIG.  1   , the display device  100  includes a display area  102  formed in an insulating surface, a scan line drive circuit  104 , a driver IC  106 , and a terminal part in which a plurality of terminals  107  is arranged. A light-emitting element having an organic layer composed of an organic material is arranged in the display area  102 . In addition, a peripheral area  103  surrounds the display area  102 . The driver IC  106  functions as a control unit that transmits a signal to the scan line drive circuit  104  and a data line drive circuit. The data line drive circuit may be arranged with a sampling switch or the like on a substrate  101  separately from the driver IC  106 . In addition, although the driver IC  106  is arranged above a flexible printed circuit (Flexible Print Circuit: FPC)  108 , the driver IC  106  may be arranged above the substrate  101 . The flexible printed circuit  108  is connected to the plurality of terminals  107  arranged in the peripheral area  103 . 
     In this case, the insulating surface is a surface of the substrate  101 . The substrate  101  supports each layer, such as the insulating layer and the conductive layer, arranged above its surface. Also, the substrate  101  may be made of an insulating material, may have an insulating surface, or an insulating film may be separately formed on the substrate  101  to form an insulating surface. The material of the substrate  101  and the material for forming the insulating film are not particularly limited as long as the insulating surface can be obtained. 
     In the display area  102  shown in  FIG.  1   , a plurality of pixels  105  is arranged in a matrix in an X-direction and Y-direction. In this specification and the like, a pixel refers to the smallest unit that enables the desired color to be displayed in the display area  102 . Each pixel  105  has a pixel circuit and a light-emitting element electrically connected to the pixel circuit. The light emitting element includes a pixel electrode, an organic layer (light-emitting part) including a light-emitting layer stacked on the pixel electrode, and a counter electrode. The light emitting elements included in the pixel  105  emit different colors from each other. For example, the pixel  105  emits a color of either a red light-emitting element, a green light-emitting element, or a blue light-emitting element. Also, the color emitted by the light-emitting element is not limited to the above three colors and may be at least one color. In this specification and the like, the component included in the red light-emitting element is indicated by R, the component included in the green light-emitting element is indicated by G, and the component included in the blue light-emitting element is indicated by B. In addition, an emission peak wavelength of the blue light-emitting element is 450 nm or more and 500 nm or less. An emission peak wavelength of the red light-emitting element is 610 nm or more and 780 nm or less. An emission peak wavelength of the green light-emitting element is 500 nm or more and 570 nm or less. 
     Each pixel  105  is electrically connected to a scan line  111  and a data line  113 . Although not shown, the pixel  105  is electrically connected to a power supply line. The scan line  111  extends along the X-direction and is electrically connected to the scan line drive circuit  104 . The data line  113  extends along the Y-direction and is electrically connected to the driver IC  106 . In addition, the driver IC  106  outputs a scan signal to the scan line  111  via the scan line drive circuit  104 . The driver IC  106  outputs a data signal corresponding to image data to the data line  113 . Inputting the scan signal and the data signal to the pixel circuit included in each pixel  105  makes it possible to perform a screen display corresponding to the image data. The pixel circuit is composed of a plurality of transistors. Typically, a thin film transistor (TFT) can be used as the transistor. However, the present invention is not limited to the thin film transistor, and any element having a current control function may be used. 
       FIG.  2    is an enlarged view of a pixel layout when the display device  100  is in a plan view, and  FIG.  3    is a cross-sectional view when the pixel layout shown in  FIG.  2    is cut along a line A 1 -A 2 .  FIG.  4    is a partially enlarged view of the cross-sectional view shown in  FIG.  3   . In the present embodiment, a configuration of a top-emission display device will be described. 
       FIG.  2    shows an area where pixels  105 R,  105 G, and  105 B are arranged. The pixel  105 R, the pixel  105 G, and the pixel  1058  are arranged side by side in the X-direction. In addition, the pixel  105 R and the pixel  105 R, the pixel  105 G and the pixel  105 G, and the pixel  105 B and the pixel  105 B are arranged side by side in the Y-direction. In  FIG.  2   , an area indicated by a solid line is an area where light-emitting layers  132 R,  132 G, and  132 B are arranged. In addition, an area surrounded by a dotted line is an area where openings  120 R,  120 G, and  120 B are arranged in the insulating layer. The insulating layer is also referred to as a barrier or bank. The openings  120 R,  120 G, and  120 B arranged in the insulating layer correspond to a light-emitting area when light-emitting elements  130 R,  130 G, and  130 B actually emit light. Also, if each of the light-emitting elements  130 R,  130 G, and  1308  is not distinguished, they will be collectively described as the light-emitting element  130 . In addition, the same applies to each component of the light-emitting elements  130 R,  130 G, and  130 B. 
       FIG.  3    shows a cross-sectional view of the pixels  105 R,  105 G, and  105 B. A plurality of transistors  110  is arranged above the substrate  101  via an insulating film  112 . The plurality of transistors  110  constitutes the pixel circuit. The transistor  110  is composed of at least a semiconductor layer  114 , a gate insulating film  115 , and a gate electrode  116 . An interlayer insulating film  121  is arranged above the transistor  110 . A source electrode or drain electrode  117  or  118  is arranged above the interlayer insulating film  121 . Each of the source electrode or drain electrode  117  or  118  is connected to the semiconductor layer  114  via a contact hole arranged in the interlayer insulating film  121 . An insulating film  122  is arranged above the interlayer insulating film  121 . The insulating film  122  can relieve any unevenness caused by the transistor  110  and the source electrode or drain electrode  117  or  118 . The plurality of transistors  110  arranged above the substrate  101 , and the interlayer insulating film  121  and the insulating film  122  arranged above the transistor  110  are formed by known materials and methods. Also, the configuration of the pixel circuit arranged below the insulating film  122  is omitted after  FIG.  4   . 
     The light-emitting element  130 R is arranged in the pixel  105 R, the light-emitting element  130 G is arranged in the pixel  105 G, and the light-emitting element  130 B is arranged in the pixel  105 B on the insulating film  122 . The light-emitting element  130 R has at least a pixel electrode  124 R, the light-emitting layer  132 R, and a counter electrode  138 . The light-emitting element  130 G has at least a pixel electrode  124 G, the light-emitting layer  132 G, and the counter electrode  138 . The light emitting element  130 B has at least a pixel electrode  124 B, the light-emitting layer  132 B, and the counter electrode  138 . A common layer  128  is arranged between the pixel electrodes  124 R,  124 G, and  124 B and the light-emitting layers  132 R,  132 G, and  132 B. A common layer  136  is arranged between the light-emitting layers  132 R,  132 G, and  132 B and the counter electrode  138 . The common layers  128  and  136  are arranged in common over the light-emitting elements  130 R,  130 G, and  130 B. In  FIG.  3   , the pixel electrodes  124 R,  124 G, and  1248  are anodes and the counter electrode  138  is a cathode. The common layer  128  includes at least one of a hole transport layer and a hole injection layer, and the common layer  136  includes at least one of an electron transport layer and an electron injection layer. Although not shown in  FIG.  3   , each of the pixel electrodes  124 R,  124 G, and  1248  is electrically connected to the transistor  110  included in the pixel circuit. 
     In the present embodiment, when the display device  100  is viewed in a plan view, a first end portion of the light-emitting layer  132 B is adjacent to a first end portion of the light-emitting layer  132 G. In addition, a second end portion of the light-emitting layer  132 B is adjacent to a first end portion of the light-emitting layer  132 R. In addition, a second end portion of the light-emitting layer  132 G is adjacent to a second end portion of the light-emitting layer  132 R. In this case, it is configured so that the dopant concentration at the second end portion of the light-emitting layer  132 G separated from a light-emitting area of the light-emitting layer  132 B is higher than the dopant concentration at the first end portion of the light-emitting layer  132 G adjacent to the first end portion of the light-emitting layer  1328 . In addition, it is configured so that the dopant concentration at the second end portion of the light-emitting layer  132 R separated from the light-emitting area of the light-emitting layer  132 B is higher than the dopant concentration at the first end portion of the light-emitting layer  132 R adjacent to the second end portion of the light-emitting layer  1328 . In other words, at the first end portion of the light-emitting layer  132 G adjacent to the first end portion of the light-emitting layer  132 B, it is configured so that a light emission start voltage of the light-emitting layer  132 G is high and a light emission start voltage of the second end portion of the light-emitting layer  132 G separated from the light-emitting area of the light-emitting layer  1328  is low. In addition, at the first end portion of the light-emitting layer  132 R adjacent to the second end portion of the light-emitting layer  1328 , it is configured so that a light emission start voltage of the light-emitting layer  132 R is high and the dopant concentration at the second end portion of the light-emitting layer  132 R separated from the light-emitting area of the light-emitting layer  132 B is low. Also, the first end portion of the light-emitting layer  1328  is preferably arranged so as to be close to the opening  120 G of the light-emitting element  130 G. In addition, the second end portion of the light-emitting layer  1328  is preferably arranged so as to be close to the opening  120 R of the light-emitting element  130 R. Also, “an end portion of a light-emitting layer” in this specification and the like means an outer edge of the light-emitting layer when the display device  100  is in a plan view. 
     As the definition of the EL display device increases, the pixel becomes closer to the pixel, and therefore, an effect of a leakage current in the transverse direction flowing between adjacent pixels increases. In the EL display device, the leakage current in the transverse direction may cause the light-emitting layer of the adjacent pixels to emit light, thereby deteriorating the quality of the EL display device. 
     Hereinafter, a mechanism of the leakage current in the transverse direction in the EL display device causing the light-emitting layer to emit light in an unintended area in adjacent pixels will be described with reference to  FIG.  12    to  FIG.  16   . Also, configurations of pixel circuits arranged below an insulating film  222  are omitted in  FIG.  12    to  FIG.  16   . 
       FIG.  12    is an enlarged view of a pixel layout when a conventional display device  200  is in a plan view, and  FIG.  13    is a cross-sectional view when the display device  200  shown in  FIG.  12    is cut along a line F 1 -F 2 . In addition,  FIG.  14    is a partially enlarged view of the cross-sectional view shown in  FIG.  13   . 
       FIG.  12    shows an area where pixels  205 R,  205 G, and  205 B are arranged. The pixel  205 R, the pixel  205 G, and the pixel  205 B are arranged side by side in the X-direction. In addition, the pixel  205 R and the pixel  205 R, the pixel  205 G and the pixel  205 G, and the pixel  205 B and the pixel  205 B are arranged side by side in the Y-direction. In  FIG.  12   , an area indicated by a solid line is an area where light-emitting layers  232 R,  232 G, and  232 B are arranged. In addition, an area surrounded by a dotted line is an area where openings  220 R,  220 G, and  220 B are arranged. The openings  220 R,  220 G, and  220 B arranged in the insulating layer correspond to light-emitting areas when light-emitting elements  230 R,  230 G, and  230 B actually emit light. Also, if each of the light-emitting element  230 R,  230 G, and  230 B are not distinguished, they will be collectively described as the light-emitting element  230 . In addition, the same applies to each component of the light-emitting elements  230 R,  230 G, and  230 B. 
     As shown in  FIG.  12   , a first end portion of the light-emitting layer  232 B is adjacent to a first end portion of the light-emitting layer  232 G. In addition, a second end portion of the light-emitting layer  232 B is adjacent to a first end portion of the light-emitting layer  232 R. In addition, a second end portion of the light-emitting layer  232 G is adjacent to a second end portion of the light-emitting layer  232 R. 
       FIG.  13    shows a cross-sectional view of the pixels  205 R,  205 G, and  205 B. The light-emitting element  230 R is arranged in the pixel  205 R, the light-emitting element  230 G is arranged in the pixel  205 G, and the light-emitting element  230 B is arranged in the pixel  205 B on the insulating film  222 . The light-emitting element  230 R has at least a pixel electrode  224 R, the light-emitting layer  232 R, and the counter electrode  238 . The light-emitting element  230 G has at least a pixel electrode  224 G, the light-emitting layer  232 G, and the counter electrode  238 . The light-emitting element  230 B has at least a pixel electrode  224 B, the light-emitting layer  232 B, and the counter electrode  238 . A common layer  228  is arranged between the pixel electrodes  224 R,  224 G, and  224 B and the light-emitting layers  232 R,  232 G, and  232 B. A common layer  236  is arranged between the light-emitting layers  232 R,  232 G, and  232 B and the counter electrode  238 . The common layers  228  and  236  are arranged in common over the light-emitting elements  230 R,  230 G, and  230 B (over the display area). In  FIG.  12    to  FIG.  14   , the pixel electrodes  224 R,  224 G, and  224 B are anodes and the counter electrode  238  is a cathode. Therefore, the common layer  228  includes at least one of the hole transport layer and the hole injection layer, and the common layer  236  includes at least one of the electron transport layer and the electron injection layer. 
     In order to suppress unintended light emission in adjacent pixels, areas arranged with the light-emitting layer are preferred to be separated from each other so as not to overlap. However, in order for the areas arranged with the light-emitting layer to be separatory formed so as not to overlap each other, the openings  220 R,  220 G, and  220 B need to be formed sufficiently separate from each other, and the definition deteriorates. 
     Therefore, as the definition of the display area is increased, the areas where the light-emitting layer is arranged may overlap. As shown in  FIG.  14   , a part of the light-emitting layer  232 G and a part of the light-emitting layer  232 B may overlap in the area where the pixel  205 G and the pixel  205 B are adjacent to each other. 
       FIG.  14    shows an enlarged view of an area  250 A where the pixel  205 G and the pixel  205 B are adjacent to each other. The light-emitting layer  232 B and the light-emitting layer  232 G are arranged above the common layer  228  on an insulating layer  226 . A part of the light-emitting layer  232 B overlaps with a part of the light-emitting layer  232 G. Generally, a light emission start voltage of the light-emitting layer  232 B is higher than light emission start voltages of the light-emitting layer  232 R and the light-emitting layer  232 G. Therefore, when the light-emitting element  230 B is caused to emit light, a high voltage is applied to the light-emitting layer  232 B, so that the holes in the common layer  228  move in the transverse direction from the pixel  205 B to the pixel  205 R and the pixel  205 G. If the light-emitting layer  232 B exhibits a hole-transport property, the holes pass through the light-emitting layer  232 B in the thickness direction. Therefore, the light-emitting layer  232 G emits light at an end portion of the light-emitting layer  232 G. Alternatively, if the light-emitting layer  232 B exhibits an electron-transport property, the hole does not pass through the light-emitting layer  232 B in the thickness direction but moves in the transverse direction. Therefore, the light-emitting layer  232 G emits light in the vicinity of the end portion of the light-emitting layer  232 B. In this specification and the like, a position where unintended light emission occurs in the light-emitting layer  232 R or the light-emitting layer  232 G adjacent to the light-emitting layer  232 B is referred to as a starting point of light emission. Also, the light emission start voltage of the light-emitting layer  232 R and the light emission start voltage of the light-emitting layer  232 G are approximately the same. Therefore, even if the light-emitting element  230 G is caused to emit light, the holes in the common layer  228  are prevented from moving in the transverse direction from the pixel  205 G to the pixel  205 R and the pixel  205 B. Therefore, an end portion of the light-emitting layer  232 R and the light-emitting layer  232 G do not emit light in an area where the end portion of the light-emitting layer  232 R overlaps the end portion of the light-emitting layer  232 G. 
     As shown in  FIG.  15   , in the area where the pixel  205 G and the pixel  205 B are adjacent to each other, a part of the light-emitting layer  232 G and a part of the light-emitting layer  232 B may be separated. 
       FIG.  16    shows an enlarged view of an area  250 B where the pixel  205 G and the pixel  205 B adjacent to each other. The light-emitting layer  232 B and the light-emitting layer  232 G are arranged above the common layer  228  on the insulating layer  226 . The end portion of the light-emitting layer  232 B is separated from the end portion of the light-emitting layer  232 G. The light emission start voltage of the light-emitting layer  232 B is higher than the light emission start voltages of the light-emitting layer  232 G and the light-emitting layer  232 R. Therefore, when the light-emitting element  230 B is caused to emit light, a high voltage is applied to the light-emitting layer  232 B, so that the holes in the common layer  228  move in the transverse direction from the pixel  205 B to the pixel  205 G and the pixel  205 R. If the light-emitting layer  232 B exhibits an electron-transport property, the holes do not pass through the light-emitting layer  232 B in the thickness direction but move in the transverse direction. Therefore, the light-emitting layer  232 G emits light even if the end portion of the light-emitting layer  232 G is separated from the end portion of the light-emitting layer  232 B. 
     As described above, since the emission start voltages of the light-emitting layers  232 R,  232 G, and  232 B are different from each other, even if the light-emitting layer  232 B overlaps or does not overlap the adjacent light-emitting layers  232 R and  232 G, a leakage current in the transverse direction occurs, and the light-emitting layer emits light in an unintended area. In order to suppress unintended light emission in each light-emitting layer, it is conceivable to prevent the leakage current in the transverse direction by designing the light emission start voltages of the light-emitting layers  232 R,  232 G, and  232 B to coincide with each other. However, it is a trade-off with the property of the light-emitting element due to the need for designs such as suppressing the property of the light-emitting element and carrier injections into the light-emitting layer. As described above, conventionally, it has been difficult to prevent unintentional light emission caused by the leakage current in the transverse direction while improving the property of the light-emitting element. 
     As described in  FIG.  12    to  FIG.  16   , the starting point of light emission differs depending on the order in which the common layer  228  and the light-emitting layers  232 R,  232 G, and  232 B are stacked. In addition, the strength of the leakage current in the transverse direction depends on a distance from the light-emitting area of the light-emitting element  230 B. Therefore, when the distance between the light-emitting area of the light-emitting element  230 B and the end portion of the light-emitting layer  232 B is designed to be small by increasing the definition, the strength of the leakage current increases. Therefore, the intensity of the unintended light emission in the light-emitting layer  232 R and the light-emitting layer  232 G arranged so as to overlap or be separated from the end portion of the light-emitting layer  232 B also increases. 
     Therefore, in the display device  100  according to an embodiment of the present invention, gradients of the light emission start voltages of the light-emitting layers  132 R and  132 G are set so that the light emission start voltage in the area where the end portions of the light-emitting layers  132 R and  132 G of the light-emitting elements  130 R and  130 G having a low light emission start voltage are adjacent to the end portion of the light-emitting layer  132 B of the light-emitting element  130 B having a higher light emission start voltage than the light-emitting elements  130 R and  130 G, that is, where the area of the light-emitting layers  132 R and  132 G adjacent to the end portion of the light-emitting layer  132 B where unintended light emission is likely to occur is high, and the light emission start voltage in the area of the light-emitting layers  132 R and  132 G separated from the light-emitting area of the light-emitting element  1328  is low. This suppresses light emission at the end portion of the light-emitting layers  132 R and  132 G. Specifically, the dopant concentration at the end portions of the light-emitting layers  132 R and  132 G adjacent to the end portion of the light-emitting layer  1328  is decreased, and the dopant concentration at the end portions of the light-emitting layers  132 R and  132 G separated from the light-emitting area of the light-emitting layer  132 B is increased. In the present embodiment, an example in which a pixel electrode functions as an anode will be described. 
     In the present embodiment, the case where the light emission start voltage of the light-emitting element  1308  is higher than the light emission start voltages of the light-emitting elements  130 R and  130 G will be described as an example. However, even when the light emission start voltage of the light-emitting element  130 R is higher than the light emission start voltages of the light-emitting elements  130 G and  1308  or when the light emission start voltage of the light-emitting element  130 G is higher than the light emission start voltages of the light-emitting elements  130 R and  130 B, it is possible to obtain the advantage according to the present embodiment by decreasing the dopant concentration at the area adjacent to the end portion of the light-emitting layer of the light-emitting element where the light emission start voltage is high and by increasing the dopant concentration at the end portion of the light-emitting layer of the light-emitting element where the light emission start voltage is low separated from the light-emitting area of the light-emitting layer of the light-emitting element where the light emission start voltage is high. 
       FIG.  4    is a partially enlarged view of the cross-sectional view shown in  FIG.  3   .  FIG.  4    shows an enlarged view of the light-emitting element  130 G. As shown in  FIG.  4   , in a cross-sectional view, a gradient is set to the dopant concentration in the light-emitting layer  132 G so that the dopant concentration in a second area  132 G- 2  at the end portion of the light-emitting layer  132 G adjacent to the light-emitting layer  132 R is higher than the dopant concentration in a first area  132 G- 1  at the end portion of the light-emitting layer  132 G adjacent to the light-emitting layer  1328 . In addition, the light-emitting layer  132 G has a third area  132 G- 3  having a third dopant concentration in an area inside the opening  120 G that is higher than a first dopant concentration in the first area  132 G- 1  and lower than a second dopant concentration in the second area  132 G- 2 . In this case, in this specification and the like, the display device  100  is cut along a plane or a curved surface intersecting the insulating surface, and a state in which the cut surface is viewed from a plane parallel to the screen is referred to as a “cross-sectional view.” 
     The first dopant concentration in the first area  132 G- 1  can be set, for example, to one-fifth or less, preferably one-tenth or less of the third dopant concentration in the third area  132 G- 3 . In addition, the second dopant concentration in the second area  132 G- 2  can be set to, for example, five-fold or more, preferably ten-fold or more of the third dopant concentration in the third area  132 G- 3 . 
     In addition, as shown in  FIG.  14   , the first area  132 G- 1  at the end portion of the light-emitting layer  132 G may be arranged so as to overlap the end portion of the light-emitting layer  132 B. Alternatively, the end portion of the light-emitting layer  1328  may be arranged so as to be close to the light-emitting area (the opening  120 G) of the light-emitting element  130 G. In  FIG.  3   , when a distance from an end portion of the opening  120 B to an end portion of the opening  120 G is d 1 , the end portion of the light-emitting layer  1328  is set to a length of d 1 / 2 . In an embodiment, the end portion of the light-emitting layer  132 B may be set to be longer than d 1 / 2 . That is, the end portion of the light-emitting layer  1328  may be arranged on a side closer to the opening  120 G than an intermediate part d 1 / 2  between the end portion of the opening  120 G and the end portion of the opening  120 B. In this case, the end portion of the opening  120 B refers to a part in contact with the pixel electrode  124 B. In addition, the end portion of the opening  120 G refers to a part in contact with the pixel electrode  124 G. 
     Although an end portion of the light-emitting layer  132 R adjacent to the light-emitting layer  1328  is not shown in detail in  FIG.  4   , it is the same as an end portion  132 B- 1  of the light-emitting layer  132 B. That is, a gradient is set to the dopant concentration in the light-emitting layer  132 R so that the dopant concentration in the second area at the end portion of the light-emitting layer  132 R adjacent to the light-emitting layer  132 G is higher than the dopant concentration in the first area at the end portion of the light-emitting layer  132 R adjacent to the light-emitting layer  1328 . In addition, the light-emitting layer  132 R has a third area having a third dopant concentration in an area inside the opening  120 R that is higher than the first dopant concentration in the first area and lower than the second dopant concentration in the second area. 
     The first dopant concentration in the first area  132 R- 1  can be set, for example, to one-fifth or less, preferably one-tenth or less of the third dopant concentration in a third area  132 R- 3 . In addition, the second dopant concentration in the second area  132 R- 2  may be set to, for example, five-fold or more, preferably ten-fold or more of the third dopant concentration in the third area  132 R- 3 . 
     In addition, the first area at the end portion of the light-emitting layer  132 R may be arranged so as to overlap the end portion of the light-emitting layer  132 B. Alternatively, the end portion of the light-emitting layer  1328  may be arranged so as to be close to the light-emitting area (the opening  120 R) of the light-emitting element  130 R. In  FIG.  3   , when a distance from the end portion of the opening  1208  to the end portion of the opening  120 G is d 2 , the end portion of the light-emitting layer  132 B is set to a length of d 2 / 2 . In an embodiment, the end portion of the light-emitting layer  1328  may be set to be longer than d 2 / 2 . That is, the end portion of the light-emitting layer  1328  may be arranged on a side closer to the opening  120 R than an intermediate part d 2 / 2  between the end portion of the opening  120 R and the end portion of the opening  1208 . 
     In this way, decreasing the dopant concentration in the light-emitting layers  132 R and  132 G adjacent to the end portion of the light-emitting layer  132 B where unintended light emission is likely to occur makes it is possible to increase the light emission start voltage in the areas of the light-emitting layers  123 R and  132 G adjacent to the end portion of the light-emitting layer  132 B, thereby reducing the leakage current in the transverse direction or the thickness direction of the light-emitting layer  132 B. As a result, it is possible to suppress the occurrence of unintended light emission in the light-emitting layer  132 R or the light-emitting layer  132 G. 
     Although not shown in  FIG.  3    and  FIG.  4   , a sealing film may be arranged above the light-emitting elements  130 R,  130 G, and  130 B. The sealing film is composed by combining an inorganic insulating film and an organic insulating film. As a result, it is possible to prevent water from entering into the organic layer including the light-emitting layer  132  and the common layers  128  and  136  in the light-emitting elements  130 R,  130 G, and  130 B. 
     &lt;Method for Manufacturing Display Device&gt; 
     A method for manufacturing the light-emitting layers  232 R,  232 G, and  232 B in the conventional display device  200  will be described.  FIG.  17    is a diagram illustrating a method for manufacturing a light-emitting layer by a vacuum deposition method.  FIG.  17    shows an example of using three deposition sources  613 - 1  to  613 - 3 . Although not shown, each layer up to the common layer  228  described in  FIG.  13    is arranged above a substrate  201 . A mask  601 G is arranged above the substrate  201  to form the light-emitting layer  232 G. The mask  601 G has an opening  603 G, and the opening  603 G is aligned on the substrate  201  at a position where the light-emitting layer  232 G is formed. In the method for manufacturing the conventional display device  200 , the inclination and/or directivity of the deposition source for the substrate  201  is controlled to stabilize a concentration distribution in the cross-sectional direction. For this reason, for example, a deposition source of a first host material is arranged in the deposition source  613 - 1 , a deposition source of a dopant is arranged in the deposition source  613 - 2 , and a deposition source of a second host material is arranged in the deposition source  613 - 3 . Arranging the deposition source in this manner makes it possible to form the light-emitting layer  232 G having a uniform dopant-concentration in a plan view and a cross-sectional view. 
     In this case, a shadow of each material from the deposition source occurs in an area surrounded by a dashed line between the substrate  201  and the mask  601 G. The shadow area is caused by differences in the shape of the mask, the distance between the deposition source and the substrate, and the angle of the deposition source with respect to the substrate. 
     In the method for manufacturing the display device  100  of the present embodiment, the arrangement of the deposition source is devised to control the distribution of the dopant concentration in the light-emitting layer to suppress the occurrence of unintended light emission in the light-emitting layer  132 R or the light-emitting layer  132 G described above. The method for manufacturing the display device  100  will be described with reference to  FIG.  5    to  FIG.  9   . 
       FIG.  5    shows an example of using three deposition sources  513 G- 1  to  513 G- 3 . Although not shown, each layer up to the common layer  128  described with reference to  FIG.  3    and  FIG.  4    is arranged above the substrate  101 . A mask  501 G is arranged above the substrate  101  to form the light-emitting layer  132 G. The mask  501 G has an opening  503 G, and the opening  503 G is aligned above the substrate  101  at a position where the light-emitting layer  132 G is formed. In the present embodiment, a dopant deposition source  513 - 1  is arranged on a side of the end portion of the light-emitting layer  132 B, a deposition source  513 - 3  of the first host material is arranged on a side of the end portion of the light-emitting layer  132 R, and a deposition source  513 - 2  of the second host material is arranged between the deposition source  513 - 1  and the deposition source  513 - 3 , preferably at a position corresponding to the surface normally passing through the center of the opening  503 G. 
     The deposition of the dopant is suppressed in the shadow area adjacent to the end portion of the light-emitting layer  1328  by arranging the deposition sources in this manner, and the first area  132 G- 1  with a low dopant concentration (or almost no dopant) is formed. On the other hand, the deposition of the first host material is suppressed (or almost no first host material) in the shadow area adjacent to the end portion of the light-emitting layer  132 R, and the dopant concentration in the second area  132 G- 2  adjacent to end portion of the light-emitting layer  132 R is higher than the first dopant concentration. In addition, the third area  132 G- 3  having the third dopant concentration that is higher than the first dopant concentration in the first area  132 G- 1  and lower than the second dopant concentration in the second area  132 G- 2  is formed in the area inside the opening  120 G. 
     Although not shown, a transistor constituting a pixel circuit is arranged above the substrate  101 . Also, a detailed description of a method for manufacturing the pixel circuit formed on the substrate  101  will be omitted because a known method for manufacturing a transistor can be applied. An interlayer insulating film containing at least one of silicon oxide and silicon nitride is formed on the transistor. A source electrode and a drain electrode are formed on the interlayer insulating film. 
       FIG.  6    is a diagram illustrating a process for forming the insulating film  122 , the pixel electrodes  124 R,  124 G, and  124 B, and an insulating layer  126 . The insulating film  122  functions as a flattening film. The insulating film  122  is made of an organic resin material. The organic resin material may be a known organic resin material such as a polyimide-based, polyamide-based, acrylic-based, epoxy-based, or siloxane-based organic resin. Arranging the insulating film  122  on the transistor or the interlayer insulating film makes it possible to relieve any unevenness of the transistor. A contact hole is formed in the insulating film  122 . 
     The pixel electrodes  124 R,  124 G, and  124 B are formed on the insulating film  122 . Each of the pixel electrodes  124 R,  124 G, and  124 B is electrically connected to the source electrode or the drain electrode connected to the transistor via the contact hole arranged in the insulating film  122 . In the present embodiment, the pixel electrodes  124 R,  124 G, and  1248  function as anodes. A highly reflective metal film is used as the pixel electrodes  124 R,  124 G, and  124 B. Alternatively, a stacked structure of a high-work-function transparent conductive layer such as an indium-oxide-based transparent conductive layer (e.g., ITO) or a zinc-oxide-based transparent conductive layer (e.g., IZO, ZnO) and the metal film is used as the pixel electrodes  124 R,  124 G, and  124 B. 
     The insulating layer  126  made of an organic resin material is formed on the pixel electrodes  124 R,  124 G, and  1248 . A known organic resin material such as a polyimide-based, polyamide-based, acrylic-based, epoxy-based, or siloxane-based organic resin material can be used. The insulating layer  126  has the openings  120 R,  120 G, and  120 B for each of a part of the pixel electrode  124 R, a part of the pixel electrode  124 G, and a part of the pixel electrode  124 B. The insulating layer  126  is arranged between the adjacent pixel electrodes  124 R,  124 G, and  1248  so as to cover end portions (edges) of the pixel electrodes  124 R,  124 G, and  1248 . The insulating layer  126  functions as a member that separates the adjacent pixel electrodes  124 R,  124 G, and  124 B. Therefore, the insulating layer  126  is also commonly referred to as a “barrier” or a “bank.” A part of the pixel electrodes  124 R,  124 G, and  124 B exposed by the openings  120 R,  120 G, and  120 B of the insulating layer  126  is the light-emitting area of the light-emitting elements  130 R,  130 G, and  130 B. The openings  120 R,  120 G, and  120 B of the insulating layer  126  are preferably such that the inner wall is a tapered shape. Therefore, when forming the common layer  128  and the light-emitting layers  132 R,  132 G, and  132 B, which will be described later, it is possible to reduce a coverage defect at the end portion of the pixel electrodes  124 R,  124 G, and  1248 . 
       FIG.  7    is a diagram illustrating a process for forming the common layer  128  and the light-emitting layer  1328 . The common layer  128  is formed on the pixel electrodes  124 R,  124 G, and  1248  and the insulating layer  126 . The common layer  128  includes at least one of the hole transport layer and the hole injection layer. Known materials may be used as the hole transport layer and the hole injection layer as appropriate. 
     The light-emitting layers  132 R,  132 G, and  132 B are preferably formed in the order of the light-emitting layer having the highest light emission start voltage. In the present embodiment, the light emission start voltage of the light-emitting layer  132 B is higher than the light emission start voltages of the light-emitting layer  132 R and the light-emitting layer  132 G. Therefore, the light-emitting layer  132 B is first formed on the common layer  128 . As shown in  FIG.  7   , the light-emitting layer  132 B is formed by arranging a mask  501 B above the substrate  101  and depositing the material via an opening  503 B. In this case, the first end portion of the light-emitting layer  132 B may be formed so as to be close to the opening  120 R arranged in the insulating layer  126 . In addition, the second end portion of the light-emitting layer  132 B may be formed so as to be close to the opening  120 G arranged in the insulating layer  126 . The light-emitting layer  132 B is preferably a light-emitting material having an electron-transport property, and a known material may be appropriately used. 
       FIG.  8    is a diagram illustrating a process for forming the light-emitting layer  132 G. The light-emitting layer  132 G is formed by arranging the mask  501 G above the substrate  101  and depositing the material via the opening  503 G. As shown in  FIG.  5   , the dopant deposition source  513 G- 1  is arranged on a side of the end portion of the light-emitting layer  132 B, the deposition source  513 G- 3  of the first host material is arranged on a side of the end portion of the light-emitting layer  132 R, and the deposition source  513 G- 3  of the second host material is arranged between the deposition source  513 G- 1  and the deposition source  513 G- 3 , preferably at a position corresponding to the surface normally passing through the center of the opening  503 G. 
     Arranging the deposition sources in this manner suppresses the deposition of the dopant in the shadow area adjacent to the end portion of the light-emitting layer  1328 , and the first area  132 G- 1  with a low dopant concentration (or almost no dopant) is formed. On the other hand, the dopant concentration in the second area  132 G- 2  adjacent to the end portion of the light-emitting layer  132 R is higher than the first dopant concentration. In addition, the third area  132 G- 3  having the third dopant concentration that is higher than the first dopant concentration in the first area  132 G- 1  and lower than the second dopant concentration in the second area  132 G- 2  is formed in the opening  120 G. 
       FIG.  9    is a diagram illustrating a process for forming the light-emitting layer  132 R. The light-emitting layer  132 R is formed by arranging a mask  501 R above the substrate  101  and depositing the material via an opening  503 R. Although not shown, similar to  FIG.  5   , the dopant deposition source is arranged on a side of the end portion of the light-emitting layer  132 B, the deposition source of the first host material is arranged on a side of the end portion of the light-emitting layer  132 R, and the deposition source of the second host material is arranged between the dopant deposition source and the deposition source of the first host material, preferably at a position corresponding to the surface normally through the center of the opening  503 G. 
     Arranging the deposition sources in this manner suppresses the deposition of the dopant in the shadow area adjacent to the end portion of the light-emitting layer  1328 , and the first area with a low dopant concentration (or almost no dopant) is formed. On the other hand, the dopant concentration in the second area adjacent to the end portion of the light-emitting layer  132 G is higher than the first dopant concentration. In addition, a third area having the third dopant concentration that is higher than the first dopant concentration in the first area and lower than the second dopant concentration in the second area is formed in the opening  120 R. 
     Although not shown, next, the common layer  136  is then formed on the light-emitting layers  132 R,  132 G, and  132 B. The common layer  136  includes at least one of the electron transport layer and the electron injection layer. Known materials may be used as the electron transport layer and the electron injection layer as appropriate. Finally, the display device  100  shown in  FIG.  3    can be formed by forming the counter electrode  138  on the common layer  136 . 
     In the present embodiment, although the case where the light-emitting layer  132 R is formed after the light-emitting layer  132 G is formed is described, the present invention is not limited to this, and either of them may be formed first. 
     In  FIG.  2   , although the structure in which the end portion of the light-emitting layer  132 R and the end portion of the light-emitting layer  132 G adjacent to each other do not overlap is shown, the end portion of the light-emitting layer  132 R and the end portion of the light-emitting layer  132 G adjacent to each other may overlap. This is because, if the light emission start voltage of the light-emitting layer  132 R and the light emission start voltage of the light-emitting layer  132 G are approximately the same, even if the light-emitting element  130 R or the light-emitting element  130 G emits light, the effect of the leakage current in the transverse direction from the light-emitting layer  132 R and the light-emitting layer  132 G is small. 
     In addition, in the present embodiment, the method for manufacturing the display device  100  has been described as exemplifying the case where the light emission start voltage of the light-emitting element  130 B is higher than the light emission start voltages of the light-emitting elements  130 R and  130 G. However, even when the light emission start voltage of the light-emitting element  130 R is higher than the light emission start voltage of the light-emitting elements  130 G and  1308  or when the light emission start voltage of the light-emitting element  130 G is higher than the light emission start voltage of the light-emitting elements  130 R and  130 B, the display device  100  according to the present embodiment can be manufactured by forming the concentration gradient of the carrier in the light-emitting layer of the light-emitting element having the low light emission start voltage so that the carrier concentration in the area adjacent to the end portion of the light-emitting layer of the light-emitting element having the high emission start voltage is low. 
     The display device  100  according to an embodiment of the present invention is not limited to the configuration shown in  FIG.  2    to  FIG.  4   . For example, the arrangement of the pixels  105 R,  105 G, and  105 B is not limited to the arrangement of the pixels  105 R,  105 G, and  105 B shown in  FIG.  2   . 
     &lt;Modification 1&gt; 
     Next, a display device  100 A according to Modification 1 in which a part of the components of the display device  100  is modified will be described with reference to  FIG.  10   . In the display device  100 A according to Modification 1, the arrangement of the light-emitting layers  132 R,  132 G, and  1328  is different from the arrangement in the display device  100 . In the following description, the same components as those of the display device  100  may be referred to in the description of  FIG.  2    to  FIG.  4   . 
       FIG.  10    is a pixel layout diagram when the display device  100 A according to an embodiment of the present invention is in a plan view. In Modification 1, the display device  100 A with a square arrangement in which the light-emitting layers  132 R and  132 G having a smaller area than the light-emitting layer  132 B are combined and arranged so as to be a rectangular shape will be described. In Modification 1, the case where the light emission start voltage of the light-emitting layer  1328  is higher than the light emission start voltages of the light-emitting layer  132 R and the light-emitting layer  132 G will be described. 
       FIG.  10    shows an area where the pixels  105 R,  105 G, and  105 B are arranged. The pixel  105 R and the pixel  105 B are arranged side by side in the X-direction. The pixel  105 G and the pixel  105 B are arranged side by side in the X-direction. The pixel  105 R and the pixel  105 G are arranged side by side in the Y-direction. In  FIG.  10   , an area indicated by a solid line is an area where the light-emitting layers  132 R,  132 G, and  132 B are arranged. In addition, an area surrounded by a dotted line is an area where the openings  120 R,  120 G, and  1208  are arranged in the insulating layer. Also, in the display device  100 A, the stacking order of the light-emitting layers  132 R,  132 G, and  1328  is the same as in the display device  100 . 
     In the display device  100 A, light emission at the end portions of the light-emitting layer  132 R and  132 G is suppressed by setting the gradient of the light emission start voltage in the area of the light-emitting layers  132 R and  132 G so that the light emission start voltage in the area of the light-emitting layers  132 R and  132 G adjacent to the end portion of the light-emitting layer  132 B where unintended light emission is likely to occur is high and the light emission start voltage in the area of the light-emitting layers  132 R and  132 G separated from the light-emitting layer  1328  is low. In the display device  100 A, since the pixel  105 R and the pixel  105 G are arranged to be sandwiched by two pixels  1058  arranged in the X-direction, the areas adjacent to the end portion of the light-emitting layer  1328  exist in two opposing end portions. Therefore, it is impossible to have a structure in which the dopant concentration in the area adjacent to the end portion of the light-emitting layer  132 B is decreased and the dopant concentration at the opposing end portion is increased as described in the display device  100 . 
     In this modification, at the end portion of the light-emitting layer  132 B, it is possible to reduce the strength of the leakage current in the transverse direction from the light-emitting layer  132 B by decreasing the dopant concentration in the area where the light-emitting layer  312 R and the light-emitting layer  132 G which are close to the center of the light-emitting layer  132 B, that is, the center of the opening  120 B, are adjacent to, and increasing the dopant concentration in the area separated from the center of the light-emitting layer  132 B opposed to that area. As a result, it is possible to suppress the occurrence of unintended light emission in the light-emitting layer  132 R or the light-emitting layer  132 G. 
     In addition, the present modification may be applied in the case where the light emission start voltage of the light-emitting layer  132 R is higher than the light emission start voltages of the light-emitting layer  132 G and the light-emitting layer  132 B, or in the case where the light emission start voltage of the light-emitting layer  132 G is higher than the light emission start voltages of the light-emitting layer  132 R and the light-emitting layer  132 B. 
     If the emission start voltage of the light-emitting layer  132 R is higher than the emission start voltages of the light-emitting layer  132 G and the light-emitting layer  132 B, the leakage current in the transverse direction from the light-emitting layer  130 R can be reduced at the end portion of the light-emitting layer  312 R by decreasing the dopant concentration in the area where the light-emitting layer  132 G close to the center of the light-emitting layer  132 R, that is, the center of the opening  120 R, is adjacent to and the area where the light-emitting layer  132 B is adjacent to and increasing the dopant concentration in the area separated from the center of the light-emitting layer  132 R opposed to each area. As a result, it is possible to suppress the occurrence of unintended light emission in the light-emitting layer  132 G or the light-emitting layer  1328 . 
     In addition, when the light emission start voltage of the light-emitting layer  132 G is higher than the light emission start voltages of the light-emitting layer  132 R and the light-emitting layer  132 B, the leakage current in the transverse direction from the light-emitting element  130 G can be reduced at the end portion of the light-emitting layer  132 G by decreasing the dopant concentration in the area where the light-emitting layer  312 R close to the center of the light-emitting layer  312 G, that, is, the center of the opening  120 G, is adjacent to and increasing the dopant concentration in the area separated from the center of the light-emitting layer  132 G opposed to each area. As a result, it is possible to suppress the occurrence of unintended light emission in the light-emitting layer  132 R or the light-emitting layer  132 B. 
     &lt;Modification 2&gt; 
     In the present embodiment and Modification 1, an example in which a pixel electrode functions as an anode has been described. Pixel electrodes  144 R,  144 G, and  144 B can function as cathodes as Modification 2. 
       FIG.  11    shows a cross-sectional view when a display device  100 B is cut along a line A 1 -A 2 . The display device  1008  of Modification 2 is different from the display device  100  in that the pixel electrodes  144 R,  144 G, and  144 B function as cathodes and a counter electrode  158  functions as an anode. The common layer  148  arranged between the pixel electrodes  144 R,  144 G, and  144 B and the light-emitting layers  132 R,  132 G, and  1328  includes at least one of the electron transport layer and the electron injection layer. In addition, the common layer  156  arranged between the counter electrode  158  and the light-emitting layers  132 R,  132 G, and  132 B includes at least one of the hole transport layer and the hole injection layer. Also, each of the pixel electrodes  144 R,  144 G, and  144 B is electrically connected to the transistor  110  included in the pixel circuit. 
     In the display device  1008  of Modification 2, the pixel electrode  144  is used as a cathode, and the counter electrode  158  is used as an anode in the light-emitting element  130 . Even in this case, similar to the display device  100 , the leakage current in the transverse direction or the thickness direction of the light-emitting layer  132 B can be reduced by decreasing the dopant concentration in the area of the light-emitting layers  132 R and  132 G adjacent to the end portion of the light-emitting layer  132 B where unintended light emission is likely to occur to increase the light emission start voltage in the area of the light-emitting layers  132 R and  132 G adjacent to the end portion of the light-emitting layer  132 B. As a result, it is possible to suppress the occurrence of unintended light emission in the light-emitting layer  132 R or the light-emitting layer  132 G. 
     In addition, the configuration of the display device  100 B according to Modification 2 can be applied to the configuration according to the display device  100 A according to Modification 1. That is, in the display device  100 A according to Modification 1, the pixel electrode  124  may be used as a cathode, and the counter electrode  138  may be used as an anode. In this case, a common layer arranged between the pixel electrode  124  and the light-emitting layer  132  includes at least one of the electron transport layer and the electron injection layer. In addition, the common layer arranged between the counter electrode  138  and the light-emitting layer includes at least the hole transport layer and the hole injection layer. The light-emitting layer having the highest light emission start voltage among the light-emitting layers  132 R,  132 G, and  1328  is preferably arranged above the common layer  128  including the electron transport layer and the electron injection layer. The light-emitting layer is preferably composed of a light-emitting material having a hole-transport property. 
     As described above, the display device according to an embodiment of the present invention can be applied to various forms. Therefore, the addition, deletion, or design change of components, or the addition, deletion, or condition change of processes as appropriate by those skilled in the art based on the display devices  100 ,  100 A to  100 F described as the embodiments and modifications of the present invention are also included in the scope of the present invention as long as they are provided with the gist of the present invention. Further, each of the embodiments described above as an embodiment of the present invention can be appropriately combined and implemented as long as no contradiction is caused. 
     Although the above-described embodiment mainly describes the display device having the organic EL element as a display element that suppresses a leakage current in the organic layer, the present invention is applicable not only to a display device but also to an optical sensor device or the like configured by arranging an organic photodiode in which an organic layer is sandwiched between electrodes in a matrix. More specifically, the present invention can be applied to the end portion of the organic layers forming the organic photodiode, which are separately formed. Also, the present invention can be applied to a configuration in which the end portions of the organic layers forming the organic photodiode overlap. 
     Further, it is understood that, even if the effect is different from those provided by each of the above-described embodiments, the effect obvious from the description in the specification or easily predicted by persons ordinarily skilled in the art is apparently derived from the present invention.