Patent Publication Number: US-2017357125-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese application JP2016-117318 filed on Jun. 13, 2016, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device. 
     2. Description of the Related Art 
     In a display device such as an organic Electro Luminescence (EL) display, a light-emitting element, such as an organic light emitting diode (OLED), may be controlled by using a switching element, such as a transistor, to display an image. 
     Japanese Patent Laid-open Publication No. 2006-164543 discloses a sealing film of an organic EL element, the sealing film including a barrier layer made of silicon nitride and a stress relaxation layer made of at least either one of silicon oxynitride and silicon oxide. 
     Japanese Patent Laid-open Publication No. 2009-037811 discloses a manufacturing method for manufacturing an organic EL device in which an inorganic film of one layer in a sealing layer is formed using an ion beam sputtering method and other inorganic films in the sealing layer are formed using a method other than the ion beam sputtering method. 
     Japanese Patent No. 4729759 discloses a sealing film for an organic EL device, the sealing layer having a laminated structure containing at least three layers including alternately laminates silicon nitride film and silicon oxynitride film. 
     An organic EL display device may include a sealing film for protecting an organic layer. A sealing film may have a structure containing an inorganic insulating film with a small water permeability and an organic insulating film covering a foreign matter. In this case, light may reflect at the interface between the inorganic insulating film and the organic insulating film due to a difference in the refractive index between respective materials forming these films. This may deteriorate light extraction efficiency of the organic EL display device. 
     SUMMARY OF THE INVENTION 
     The object of the preset invention is to provide a display device with reduced light reflection in a sealing layer and improved light extraction efficiency. 
     A display device according to the present invention includes a pixel electrode formed on an insulating surface; an organic layer including a light emitting layer and formed on the pixel electrode; an opposed electrode formed on the organic laver; a first inorganic insulating film formed on the opposed electrode; a first intermediate film formed on the first inorganic insulating film; and first organic insulating film formed on the first intermediate film, wherein the refractive index of the first intermediate film is less than the refractive index of the first inorganic insulating film and greater than the refractive index of the first organic insulating film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an organic EL display device according to an embodiment of the present invention; 
         FIG. 2  is a wiring diagram of an organic EL panel according to an embodiment of the present invention; 
         FIG. 3  is a circuit diagram of a pixel of an organic EL panel according to an embodiment of the present invention; 
         FIG. 4  is a cross sectional view of a pixel of an organic EL panel according to an embodiment of the present invention; 
         FIG. 5  is an enlarged view of a cross section of a pixel of an organic EL panel according to an embodiment of the present invention; 
         FIG. 6  illustrates first to third examples of a correlation between a light wavelength and a reflectance of a first inorganic insulating film, a first intermediate film, and a first organic insulating film of an organic EL panel according to an embodiment of the present invention; 
         FIG. 7  illustrates a correlation between a reflectance and a light wavelength in a first comparative example; 
         FIG. 8  illustrates fourth to sixth examples of a correlation between a light wavelength and a reflectance of a first organic insulating film, a second intermediate film, a second inorganic insulating film, a third intermediate film, and a second organic insulating film of an organic EL panel according to an embodiment of the present invention; 
         FIG. 9  illustrates seventh to ninth examples of a correlation between a light wavelength and a reflectance of a first organic insulating film, a second intermediate film, a second inorganic insulating film, a third intermediate film, and a second organic insulating film of an organic EL panel according to an embodiment of the present invention; and 
         FIG. 10  illustrates a correlation between a reflectance and a light wavelength in second to fourth comparative examples. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following describes an embodiment of the present invention with reference to the drawings. The disclosure is a mere example, and naturally any modification readily conceived by a person skilled in the art without departing from the gist of the present invention will be included in the range of the present invention. The drawings may illustrate the widths, thicknesses, shapes, or the like, of the respective units more schematically for clarity of explanation as compared with actual aspects. These are mere examples, and should not limit interpretation of the present invention in any way. In this specification and respective drawings, an element similar to that which has been described earlier in connection with a drawing mentioned earlier is given the same reference numeral, and a duplicated description is avoided. 
       FIG. 1  is a perspective view of an organic EL display device  1  according to an embodiment of the present invention. The organic EL display device  1  includes an organic EL panel  10  fixedly sandwiched by an upper frame  2  and a lower frame  3 . The organic EL panel  10  is driven by an external drive circuit, which may be provided inside, that is, between, the upper frame  2  and the lower frame  3 , together with the organic EL panel  10 , or provided outside via a lead line. 
       FIG. 2  is a wiring diagram of the organic EL panel  10  according to an embodiment of the present invention.  FIG. 3  is a circuit diagram of a pixel of the organic EL panel  10  according to an embodiment of the present invention. The organic EL panel  10  controls respective pixels arranged in a matrix on a display area  11  on a substrate  20 , using a video signal drive circuit  12  and a scan signal drive circuit  13 , to display an image. The video signal drive circuit  12  is a circuit that generates a video signal to be sent to each pixel, and sends the signal. The scan signal drive circuit  13  generates a scan signal to be sent to a thin film transistor (TFT) formed in each pixel, and sends the signal. The video signal drive circuit  12  and the scan signal drive circuit  13 , which are illustrated as formed in two respective positions in  FIG. 2 , may be formed in a single integrated circuit (IC) or formed separately in three or more positions. 
     The signal from the scan signal drive circuit  13  is transmitted via a scan signal line  14 , which is electrically connected to the gate of a pixel transistor SST formed in each pixel area. The scan signal line  14  is common to the pixel transistors aligned in one row. The pixel transistor SST is a transistor electrically connected via its source or drain to the gate of a drive transistor DRT. The drive transistor DRT is an electric field effect transistor having an n-type channel, for example, with the source thereof electrically connected to the anode of an organic light emitting diode OLED. The cathode of the organic light emitting diode OLED is fixed at the ground potential or negative potential. In the above, a current flows from the anode to cathode in the organic light emitting diode OLED. Meanwhile, the signal from the video signal drive circuit  12  is transmitted via a video signal line  15 , which is electrically connected to either the source or drain of the pixel transistor SST. The video signal line  15  is common to the pixel transistors aligned in a single column. With a scan signal applied to the scan signal line  14 , the pixel transistor SST is turned on. With a video signal applied to the video signal line  15  while the pixel transistor SST is in an on state, a video signal voltage is applied to the gate of the drive transistor DRT, whereby a voltage in accordance with the video signal is written into the holding capacitor Cs, and the drive transistor DRT is turned on. Here, note that the drain of the drive transistor DRT is electrically connected to a power supply line  16 , to which a power supply voltage for causing the organic light emitting diode OLED to emit light is applied. Thus, with the drive transistor DRT turned on, a current in accordance with the video signal voltage flows into the organic light emitting diode OLED, which then emits light. 
       FIG. 4  is a cross sectional view of a pixel of the organic EL panel  10  according to an embodiment of the present invention. This drawing is a cross sectional view of a pixel along the line IV-IV shown in  FIG. 2 . In the organic EL panel  10  according to this embodiment, a first insulating film  21  is formed on the substrate  20 , and a channel of the drive transistor DRT is formed on the first insulating film  21 . A second insulating film  22  is formed on the first insulating film  21 , and a gate of the drive transistor DRT is formed on the second insulating film  22 . A third insulating film  23  is formed on the second insulating film  22 , and a fourth insulating film  24  is formed on the third insulating film  23 . Each of the second insulating film  22 , the third insulating film  23 , and the fourth insulating film  24  has a through-hole formed therein. In the through-hole, a source electrode and a drain electrode are formed that are electrically connected to the channel of the drive transistor DRT. 
     A planarization film  25  is formed on the fourth insulating film  24 . In the organic EL panel  10  according to this embodiment, the planarization film  25  is made of organic insulating material and has an insulating surface. A pixel electrode  30  is formed on the upper surface of the planarization film  25 . That is, the upper surface of the planarization film  25  is an insulating surface, and the pixel electrode  30  is formed on the insulating surface. A bank  36  is formed on the pixel electrode  30  and the planarization film  25 . The bank  36  has an opening formed therein at a position overlapping the pixel electrode  30 , and the pixel electrode  30  is partially exposed through the opening. In the opening of the bank  36 , an organic layer  31  including a light emitting layer is formed in contact with the exposed part of the pixel electrode  30 . That is, the organic layer  31  is formed on the pixel electrode  30 , and covers the opening of the bank  36 . An opposed electrode  32  is formed on the organic layer  31 . The opposed electrode  32  is made of material that allows the light emitted from the organic layer  31  to pass through. The opposed electrode  32  is formed on the organic layer  31  and the bank  36 . A sealing film  33  is formed on the opposed electrode  32 . A filler  34  is applied onto the sealing film  33 . An opposed substrate  35  is fixedly formed on the filler  34 . 
       FIG. 5  is an enlarged view of a cross section of a pixel of the organic EL panel according to an embodiment of the present invention. This drawing illustrates a laminated structure of the sealing film  33 . In particular, a first inorganic insulating film  40   a  having a film thickness d 1  and a refractive index n 1  is formed on the opposed electrode  32 . A first intermediate film  41   a  having a film thickness d 2  and a refractive index n 2  is formed on the first inorganic insulating film  40   a.  A first organic insulating film  42   a  having a film thickness d 3  and a refractive index n 3  is formed on the first intermediate film  41   a.  The refractive index n 2  of the first intermediate film  41   a  is less than the refractive index n 1  of the first inorganic insulating film  40   a  and greater than the refractive index n 3  of the first organic insulating film  42   a.  That is, the correlation n 1 &gt;n 2 &gt;n 3  is held. 
     In the organic EL panel  10  according to this embodiment, the first inorganic insulating film  40   a  is made using a silicon nitride film and has the refractive index n 1 =1.9. The first intermediate film  41   a  is made using a silicon oxynitride film and has the refractive index n 2 =1.7. The first organic insulating film  42   a  is made of resin containing acrylic or epoxy, and has the refractive index n 3 =1.5. Note that the materials and the respective values of the refractive indexes mentioned above of the first inorganic insulating film  40   a,  the first intermediate film  41   a,  and the first organic insulating film  42   a  are mere examples, and any other materials that hold the correlation n 1 &gt;n 2 &gt;n 3  can be used. 
       FIG. 6  illustrates first to third examples of the correlation between the light wavelength and the reflectance of the first inorganic insulating film  40   a,  the first intermediate film  41   a,  and the first organic insulating film  42   a  of the organic EL panel  10  according to an embodiment of the present invention. This drawing illustrates a first example in which the film thickness of the first inorganic insulating film  40   a  is 1 μm, or d 1 =1 μm, that of the first organic insulating film  42   a  is 10 μm, or d 3 =10 μm, and that of the first intermediate film  41   a  is 60 nm, or d 2 =60 nm, a second example width d 2 =75 nm, and the third example with d 2 =90 nm. Each graph shows a light reflectance (%) with respect to a light wavelength between 350 nm and 750 nm. Note that the light reflectance here refers to the percentage of the light reflected toward the organic layer  31  side by the first inorganic insulating film  40   a,  the first intermediate film  41   a,  and the first organic insulating film  42   a,  in relation to the visible light emitted from the organic layer  31  toward the display surface side of the organic EL panel  10 . In each graph, the wavelength range for blue (420 nm to 440 nm in this specification), that for green (525 nm to 545 nm in this specification) and that for red (620 nm to 640 nm) are shown hatched. 
     In the organic EL panel  10  according to this embodiment, the reflectance of the visible light emitted from the organic layer  31  toward the display surface side and reflected by the first inorganic insulating film  40   a,  the first intermediate film  41   a,  and the first organic insulating film  42   a  changes along a downward convex curve in relation to the wavelength, and takes the minimum value in the visible light wavelength range. In the first example, shown at the top in  FIG. 6 , the reflectance changes along a downward convex curve in relation to the wavelength, and takes the minimum value (0%) in the blue wavelength range. The reflectance in the first example is equal to or less than 0.5% in the green and red respective wavelength ranges, and takes a very small value over the entire visible light region. 
     In the second example, shown at the middle in  FIG. 6 , the reflectance changes along a downward convex curve in relation to the wavelengths, and takes the minimum value (0%) in the green wavelength range. The reflectance in the second example is equal to or less than 0.5% in the blue and red respective wavelength ranges, and takes a vary small value in the entire visible light region. Similarly, in the third example, shown at the bottom in  FIG. 6 , the reflectance changes along a downward convex curve in relation to the wavelength, and takes the minimum value (0%) in the red wavelength range. The reflectance in the third example is equal to or less than 0.5% in the blue and green respective wavelength ranges, and takes a very small value in the entire visible light region. 
     According to the organic EL panel  10  according to this embodiment, as the first intermediate film  41   a  is formed between the first inorganic insulating film  40   a  and the first organic insulating film  42   a  to hold the refractive index correlation n 1 &gt;n 2 &gt;n 3  between the respective materials forming the first inorganic insulating film  40   a,  the first intermediate film  41   a,  and the first organic insulating film  42   a,  a very small reflectance is achieved over the entire visible light region, as shown in  FIG. 6 , even when the film thickness d 2  of the first intermediate film  41   a  varies by about ±20%. This is because the first intermediate film  41   a  reduces the gap in the refractive index between the first inorganic insulating film  40   a  and the first organic insulating film  42   a  to thereby reduce reflection at the interface. This enables reduction of reflectance in the visible light region independently of the accuracy in a film forming process, and thus can improve the light extraction efficiency. Additionally, in the case where the accuracy in a film forming process is so high that it is possible to control the film thickness d 2  of the first intermediate film  41   a  within the range of about ±5%, it is possible to selectively improve the light extraction efficiency for a partial wavelength band in the visible light region. For example, light extraction efficiency for blue, whose brightness may become lower as compared with those of green and red, can be selectively improved. 
     According to the organic EL panel  10  according to this embodiment, as the reflectance changes along a downward convex curve in relation to the wavelength and takes the minimum value in the visible light wavelength range, the reflectance will not change significantly even when the film thicknesses and the refractive indexes of the first inorganic insulating film  40   a,  the first intermediate film  41   a,  and the first organic insulating film  42   a  should deviate from the design values by a few percentages, and the reflectance in the visible light region becomes 0.5% or below. 
       FIG. 7  illustrates a correlation between the reflectance and the light wavelength in a first comparative example. The first comparative example is related to a structure resulting from removing the first intermediate film  41   a  from the sealing film  33  of the organic EL panel  10  according to this embodiment so that the first inorganic insulating film  40   a  with the film thickness d 1  and the refractive index n 1  is formed on the opposed electrode  32 , and the first organic insulating film  42   a  with the film thickness d 3  and the refractive index n 3  is formed on the first inorganic insulating film  40   a.  Specifically, the film thickness d 1  of the first inorganic insulating film  40   a  is 1000 nm, or d 1 =100 nm, and the refractive index n 1  of the same is 1.9, or n 1 =1.9; the film thickness d 3  of the first organic insulating film  42   a  is 10 μm, or d 3 =10 μm and the refractive index n 3  of the same is 1.5, or n 3 =1.5. 
     In the first comparative example, the reflectance in the visible light region is 1 to 2%, which is large as compared with that of the organic EL panel  10  according to this embodiment. Although changing along a downward convex curve in relation to the wavelength, the reflectance monotonically decreases with respect to a longer wavelength and does not take the minimum value in the visible light region. Thus, when the film thicknesses and refractive indexes of the first inorganic insulating film  40   a  and first organic insulating film  42   a  should deviate from the respective design values by a few percentages, the reflectance may unintendedly become large, which may possibly deteriorate the light extraction efficiency. On the contrary, the organic EL panel  10  according to this embodiment can reduce the reflectance in the visible light region to 0.5% or below, with little possibility that the reflectance unintendedly becomes large. The enables stable increase in the light extraction efficiency. 
     Returning to  FIG. 5 , the laminated structure of the sealing film  33  will be further described with reference this drawing. On the first organic insulating film  42   a,  a second intermediate film  41   b  having a film thickness d 4  and a refractive index n 4  is formed. A second inorganic insulating film  40   b  having a film thickness d 5  and a refractive index n 5  is formed on the second intermediate film  41   b.  A third intermediate film  41   c  having a film thickness d 6  and a refractive index n 6  is formed on the second inorganic insulating film  40   b.  A second organic insulating film  42   b  having a film thickness d 7  and a refractive index n 7  is formed on the third intermediate film  41   c.  The refractive index n 4  of the second intermediate film  41   b  is less than the refractive index n 5  of the second inorganic insulating film  40   b  and greater than the refractive index n 3  of the first organic insulating film  42   a.  That is, the correlation n 5 &gt;n 4 &gt;n 3  is held. The refractive index n 6  of the third intermediate film  41   c  is less than the refractive index n 5  of the second inorganic insulating film  40   b  and greater than the refractive index n 7  of the second organic insulating film  42   b.  That is, the correlation n 5 &gt;n 6 &gt;n 7  is held. 
     In the organic EL panel  10  according to this embodiment, the second inorganic insulating film  40   b  is made using a silicon nitride film and has the refractive index n 5 =1.9. The second intermediate film  41   b  and the third intermediate film  41   c  are each made using a silicon oxynitride film, and have the refractive indexes n 4 =1.7 and n 6 =1.7. The second organic insulating film  42   b  is made of one kind of resin selected from the group consisting of resin including acrylic or epoxy, polyimide, polyethylene naphthalate, and polyethylene terephthalate, and has the refractive index n 7 =1.5. Note that the respective materials and the respective values of the refractive indexes mentioned above of the second intermediate film  41   b,  the second inorganic insulating film  40   b,  the third intermediate film  41   c,  and the second organic insulating film  42   b  are mere examples, and any other materials holding the correlation n 5 &gt;n 4 &gt;n 3  and n 5 &gt;n 6 &gt;n 7  may be usable. 
       FIG. 8  illustrates fourth to sixth examples of the correlation between the light wavelength and the reflectance of the first organic insulating film  42   a,  the second intermediate film  41   b,  the second inorganic insulating film  40   b,  the third intermediate film  41   c,  and the second organic insulating film  42   b  of the organic EL panel  10  according to the embodiment of the present invention. This drawing illustrates the fourth to sixth examples in which the film thickness d 4  of the second intermediate film  41   b  and the film thickness d 6  of the third intermediate film  41   c  are varied. In the fourth to sixth examples, the film thickness d 3  of the first organic insulating film  42   a,  the film thickness d 5  of the second inorganic insulating film  40   b,  and the film thickness d 7  of the second organic insulating film  42   b  are constant. Specifically, the film thickness d 3  of the first organic insulating film  42   a  is 10 μm, or d 3 =10 μm; the film thickness d 5  of the second inorganic insulating film  40   b  is 1 μm, or d 5 =1 μm; the film thickness d 7  of the second organic insulating film  42   b  is 5 μm, or d 7 =5 μm. The fourth example, shown at the top in  FIG. 8 , is related to a case in which the film thickness d 4  of the second intermediate film  41   b  is 90 nm, or d 4 =90 nm, and the film thickness d 6  of the third intermediate film  41   c  is 90 nm, or d 6 =90 nm. The fifth example, shown at the middle in  FIG. 8 , relates to a case in which the film thickness d 4  of the second intermediate film  41   b  is 75 nm, or d 4 =75 nm, and the film thickness d 6  of the third intermediate film  41   c  is 75 nm, or d 6 =75 nm. The sixth example, shown at the bottom in  FIG. 8 , relates to a case in which the film thickness d 4  of the second intermediate film  41   b  is 60 nm, or d 4 =60 nm, and the film thickness d 6  of the third intermediate film  41   c  is 60 nm, or d 6 =60 nm. Each graph shows a light reflectance (%) with respect to a light wavelength between 350 nm and 750 nm. Note that the light reflectance here refers to the percentage of the light reflected toward the organic layer  31  side by the first organic insulating film  42   a,  the second intermediate film  41   b,  the second inorganic insulating film  40   b,  the third intermediate film  41   c,  and the second organic insulating film  42   b  in relation to the visible light emitted from the organic layer  31  toward the display surface side of the organic EL panel  10 . In each graph, the wavelength range for the blue (420 nm to 440 nm in this specification), that for green (525 nm to 545 nm in this specification) and that for red (620 nm to 640 nm) are shown hatched. 
     In the organic EL panel  10  according to this embodiment, the reflectance of the visible light emitted from the organic layer  31  toward the display surface side and reflected by the first organic insulating film  42   a,  the second intermediate film  41   b,  the second inorganic insulating film  40   b,  the third intermediate film  41   c,  and the second organic insulating film  42   b  vibrates in relation to the wavelength, and the amplitude of vibration takes the minimum value in the visible light wavelength range. In the fourth example, shown at the top in  FIG. 8 , the reflectance vibrates in relation to the wavelength, and the amplitude of vibration takes the minimum value in the wavelength range for red. The reflectance in the fourth example is equal to or less than 2% in the wavelength range for blue, equal to or less than 0.5% in the wavelength range for green, and about 0% in the wavelength range for red, and takes a small value over the entire visible light region. 
     In the fifth example, shown at the middle in  FIG. 8 , the reflectance vibrates in relation to the wavelength, and the amplitude of vibration takes the minimum value in the wavelength range for green. The reflectance in the fifth example is equal to or less than 0.5% in the wavelength range for blue, about 0% in the wavelength range for green, and equal to or less than 0.5% in the wavelength range for red, and takes a small value over the entire visible light region. In the sixth example, shown at the bottom in  FIG. 8 , the reflectance vibrates in relation to the wavelength, and the amplitude of vibration takes the minimum value in the wavelength range for blue. The reflectance in the sixth example is about 0% in the wavelength range for blue, equal to or less than 1% in the wavelength range for green, and equal to or less than 1.5% in the wavelength range for red, and takes a small value over the entire visible light region. 
     As illustrated in  FIG. 8 , according to the organic EL panel  10  according to this embodiment, as the second intermediate film  41   b  is formed between the first organic insulating film  42   a  and the second inorganic insulating film  40   b,  and the third intermediate film  41   c  is formed between the second inorganic insulating film  40   b  and the second organic insulating film  42   b,  to hold the correlation n 5 &gt;n 4 &gt;n 3 , and n 5 &gt;n 6 &gt;n 7 , a small reflectance is achieved over the entire visible light region even when the film thickness d 4  of the second intermediate film  41   b  and the film thickness d 6  of the third intermediate film  41   c  should vary by about ±20%. This is because the second intermediate film  41   b  reduces the gap in the refractive index between the first organic insulating film  42   a  and the second inorganic insulating film  40   b  to thereby reduce reflection at the interface, and the third intermediate film  41   c  reduces the gap in the refractive index between the second inorganic insulating film  40   b  and the second organic insulating film  42   b  to thereby reduce reflection at the interface. This enables reduction of reflectance in the visible light region independently of the accuracy in a film forming process, and thus can improve the light extraction efficiency. Additionally, in the case where the accuracy in film forming process is so high that it is possible to control the film thickness d 4  of the second intermediate film  41   b  and the film thickness d 6  of the third intermediate film  41   c  within the range of about ±5%, it is possible to selectively improve the light extraction efficiency for a partial wavelength band in the visible light region. For example, light extraction efficiency for blue, whose brightness may become lower as compared with those of green and red, can be selectively improved. 
     According to the organic EL panel  10  according to this embodiment, as the reflectance vibrates in relation to the wavelength and the amplitude of vibration takes the minimum value in the visible light wavelength range, the reflectance will not change significantly even when the film thicknesses and refractive indexes of the first organic insulating film  42   a,  the second inorganic insulating film  40   b,  and the second organic insulating film  42   b  should deviate from the design values by a few percentages, and the reflectance in the visible light region becomes 2% or below. 
       FIG. 9  illustrates seventh to ninth examples of the correlation between the light wavelength and the reflectance of the first organic insulating film  42   a,  the second intermediate film  41   b,  the second inorganic insulating film  40   b,  the third intermediate film  41   c,  and the second organic insulating film  42   b  of the organic EL panel  10  according to an embodiment of the present invention. This drawing illustrates the seventh to ninth examples in which the film thickness d 5  of the second inorganic insulating film  40   b  are varied. In the respective examples, the film thickness d 3  of the first organic insulating film  42   a,  the film thickness d 4  of the second intermediate film  41   b,  the film thickness d 6  of the third intermediate film  41   c,  and the film thickness d 7  of the second organic insulating film  42   b  are constant. Specifically, the film thickness d 3  of the first organic insulating film  42   a  is 10 μm, or d 3 =10 μm, the film thickness d 4  of the second intermediate film  41   b  is 74 nm, or d 4 =75 nm, the film thickness d 6  of the third intermediate film  41   c  is 75 nm, or d 6 =75 nm, and the film thickness d 7  of the second organic insulating film  42   b  is 5 μm, or d 7 =5 μm. The seventh example, shown at the top in  FIG. 9 , is related to a case in which the film thickness d 5  of the second inorganic insulating film  40  is 1.1 μm, or d 5 =1.1 μm. The eighth example, shown at the middle in  FIG. 9 , relates to a case in which the film thickness d 5  of the second inorganic insulating film  40   b  is 1 μm, or d 5 =1 μm. The ninth example, shown at the bottom in  FIG. 9 , relates to a case in which the film thickness d 5  of the second inorganic insulating film  40   b  is 900 nm, or d 5 =900 nm. Each graph shows a light reflectance (%) with respect to a light wavelength between 350 nm and 750 nm. Note that the light reflectance here refers to the percentage of the light reflected toward the organic layer  31  side by the first organic insulating film  42   a,  the second intermediate film  41   b,  the second inorganic insulating film  40   b,  the third intermediate film  41   c,  and the second organic insulating film  42   b  in relation to the visible light emitted from the organic layer  31  toward the display surface side of the organic EL panel  10 . In each graph, the wavelength range for blue (420 nm to 440 nm in this specification), that for green (525 nm to 545 nm in this specification) and that for red (620 nm to 640 nm) are shown hatched. 
     In any of the seventh, eighth, and ninth examples shown at the top, middle, bottom in  FIG. 9 , respectively, the reflectance vibrates in relation to the wavelength and the amplitude of vibration takes the minimum value in the wavelength range for green. The reflectance in the seventh to ninth examples are equal to or less than 0.5% in the wavelength range for blue, about 0% in the wavelength range for green, and equal to or less than 0.5% in the wavelength range for red, and take a small value over the entire visible light region. 
     As illustrated in  FIG. 9 , according to the organic EL panel  10  according to this embodiment, as the correlation n 5 &gt;n 4 &gt;n 3  and n 5 &gt;n 6 &gt;n 7  is held, a small reflectance is achieved over the entire visible light region even when the film thickness d 5  of the second inorganic insulating film  40   b  should vary by about ±10%. This enables reduction of reflectance in the visible light region independently of the accuracy in a film forming process, and thus can improve the light extraction efficiency. 
       FIG. 10  illustrates a correlation between the reflectance and the light wavelength in second to fourth comparative examples. Each of the second to fourth comparative examples is related to a structure resulting from removing the second intermediate film  41   b  and the third intermediate film  41   c  from the sealing film  33  of the organic EL panel  10  according to this embodiment so that the second inorganic insulating film  40   b  with the film thickness d 5  and the refractive index n 5  is formed on the first organic insulating film  42   a  and the second organic insulating film  42   b  with the film thickness d 7  and the refractive index n 7  is formed on the second inorganic insulating film  40   b.  Specifically, the film thickness d 3  of the first organic insulating film  42   a  is 10 μm, or d 3 =10 μm, and the refractive index n 3  of the same is 1.5, or n 3 =1.5; the film thickness d 5  of the second inorganic insulating film  40   b  is 1 μm, or d 5 =1 μm, and the refractive index n 1  of the same is 1.9, or n 1 =1.9; the film thickness d 7  of the second organic insulating film  42   b  is 5 μm, or d 7 =5 μm, and the refractive index n 7  of the same is 1.5, or n 7 =1.5. In the second to fourth comparative examples, the film thickness d 5  of the second inorganic insulating film  40   b  is varied. Specifically, the film thickness d 5  of the second inorganic insulating film  40   b  in the second comparative example, shown at the top in  FIG. 10 , is 1100 nm, or d 5 =1100 nm; that in the third comparative example, shown at the middle in  FIG. 10 , is 1 μm, or d 5 =1 μm; that in the fourth comparative example, shown at the bottom in  FIG. 10 , is 900 nm, or d 5 =900 nm. 
     In the second to fourth comparative examples, the reflectance in the visible light region vibrates in the range between 0% and 5.5%. The amplitude of vibration is large as compared with that of the organic EL panel  10  according to this embodiment. Additionally, the amplitude of vibration of the reflectance in relation to change in wavelength does not take the minimum value in the visible light region. Thus, deviation of the film thickness and refractive index of the second inorganic insulating film  40   b  from the respective design values by a few percentages results in unintended increase of the reflectance, which possibly deteriorate the light extraction efficiency. With the reflectance in the wavelength range for red focused, the reflectance is 0 to 0.5% in the third comparative example, shown at the middle in  FIG. 10 , whereas the reflectance is 3 to 5.5% in the second comparative example, shown at the top in  FIG. 10 , and 3.5 to 5.5% in the fourth comparative example, shown at the bottom in  FIG. 10 . As described above, in the comparative examples, variation in the film thickness d 5  of the second inorganic insulating film  40   b  by ±10% results in variation in reflectance by about 3 to 5%. On the contrary, the organic EL panel  10  according to this embodiment can reduce the reflectance in the visible light region to 2% or below, with little possibility that the reflectance unintendedly becomes large even when the film thickness d 5  of the second inorganic insulating film  40   b  should vary by ±10%. This can stably increase the light extraction efficiency. 
     While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.