Abstract:
An organic EL display device includes: a TFT substrate that includes a display area in which pixels are arranged in a matrix; and a color filter substrate that is provided to face the TFT substrate and includes an area transmitting light in a predetermined wavelength range for each of the pixels. Each of the pixels of the TFT substrate includes a pair of electrodes, at least two light emission layers that are arranged between the pair of electrodes, and a charge generation layer that is arranged between the at least two light emission layers, is a layer to generate a pair of positive and negative charges, and has different film thicknesses in accordance with the predetermined wavelength range of the corresponding area.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese patent application JP2013-201397 filed on Sep. 27, 2013, 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 an organic EL display device. 
     2. Description of the Related Art 
     In recent years, an image display device using a self-luminous body called an organic light-emitting diode (OLED) (hereinafter referred to as an “organic EL (Electro-Luminescent) display device”) has been put to practical use. Since the self-luminous body is used, the organic EL display device is superior in terms of visibility and response speed compared to a related-art liquid crystal display device, and in addition, a further reduction in thickness is possible because an auxiliary lighting device such as a backlight is not necessary. 
     For color display in such an organic EL display device, there are primarily two kinds of methods: one is to provide light-emitting elements that respectively emit lights of three colors of R (red), G (green), and B (blue) for each pixel; and the other is to emit white light in light-emitting elements and allow lights in respective wavelength ranges of three colors of R, G, and B to transmit through color filters of pixels. 
     JP 2003-272860 A discloses an organic EL element using a charge generation layer. JP 2010-146893 A discloses an organic EL element in which a film having a high haze value is provided to improve light extraction efficiency. JP 2010-192472 A discloses an organic EL element in which the refractive index of an anode and the refractive index of a substrate are set so as to satisfy a predetermined condition to enhance light extraction efficiency. 
     SUMMARY OF THE INVENTION 
     In the organic EL display device that transmits light in the wavelength ranges of the respective colors using color filters, a phenomenon called color mixture occurs to no small extent in which light exits through a color filter of an adjacent pixel adjacent to a color filter through which the light originally exits. It is considered that such color mixture is caused by both optical color mixture and electrical color mixture. The optical color mixture occurs when light that exited in an oblique direction from a light-emitting area of a pixel exits through a color filter of an adjacent pixel. The electrical color mixture occurs when charges flow into an adjacent pixel to cause light emission in a light-emitting area of the adjacent pixel. 
     The invention has been made in view of the circumstances described above, and it is an object of the invention to provide an organic EL display device in which an influence on chromaticity is suppressed in electrical color mixture as one of the causes of color mixture. 
     An organic EL display device according to an aspect of the invention includes: a TFT (Thin Film Transistor) substrate that includes a display area in which pixels are arranged in a matrix; and a color filter substrate that is provided to face the TFT substrate and includes an area transmitting light in a predetermined wavelength range for each of the pixels, wherein each of the pixels of the TFT substrate includes a pair of electrodes, at least two light emission layers that are arranged between the pair of electrodes, and a charge generation layer that is arranged between the at least two light emission layers, is a layer to generate a pair of positive and negative charges, and has different film thicknesses in accordance with the predetermined wavelength range of the corresponding area. 
     In the organic EL display device according to the aspect of the invention, the areas of the color filter substrate may be areas that transmit lights in wavelength ranges respectively corresponding to R (red), G (green), B (blue), and W (white), and the film thickness of the charge generation layer of the pixels corresponding to W and G in the TFT substrate may be thicker than the film thickness of the charge generation layer corresponding to R and B. 
     In the organic EL display device according to the aspect of the invention, the areas of the color filter substrate may be areas that transmit lights in wavelength ranges respectively corresponding to R (red), G (green), and B (blue), and the film thickness of the charge generation layer of the pixel corresponding to G in the TFT substrate may be thicker than the film thickness of the charge generation layer corresponding to R and B. 
     In the organic EL display device according to the aspect of the invention, the two light emission layers may be composed of a light emission layer that emits light in a wavelength range corresponding to B (blue) and a light emission layer that emits light in a wavelength range corresponding to Y (yellow). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically showing an organic EL display device according to an embodiment of the invention. 
         FIG. 2  is a diagram showing the configuration of an organic EL panel in  FIG. 1 . 
         FIG. 3  is a diagram schematically showing a cross-section of a TFT substrate taken along the line III-III in  FIG. 2 . 
         FIG. 4  is a diagram schematically showing the stacked structure of an organic layer. 
         FIG. 5  is a diagram showing an organic layer in which the number of units is two. 
         FIG. 6  is a diagram showing sub-pixels constituting a pixel. 
         FIG. 7  is a diagram showing a cross-section taken along the line VII-VII in  FIG. 6 . 
         FIG. 8  is a diagram showing a cross-section taken along the line VIII-VIII in  FIG. 6 . 
         FIG. 9  is a diagram schematically showing the arrangement of a thick charge generation layer and a thin charge generation layer. 
         FIG. 10  is a diagram schematically showing the arrangement of a charge generation layer of an organic EL display device including three kinds of R, G, and B sub-pixels in each pixel as a modified example of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the invention will be described with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals and signs, and a redundant description is omitted. 
       FIG. 1  schematically shows an organic EL display device  100  according to the embodiment of the invention. As shown in the drawing, the organic EL display device  100  is composed of an organic EL panel  200  fixed so as to be interposed between an upper frame  110  and a lower frame  120 . 
       FIG. 2  shows the configuration of the organic EL panel  200  in  FIG. 1 . The organic EL panel  200  includes two substrates, a TFT (Thin Film Transistor) substrate  220  and a color filter substrate  230 . A space between the substrates is filled with a transparent resin (not shown). The TFT substrate  220  includes pixels  280  arranged in a matrix in a display area  202 . Moreover, in the embodiment, each of the pixels  280  includes four sub-pixels. The TFT substrate  220  includes a driver IC (Integrated Circuit)  260  as a driver circuit that applies, to a scanning signal line (not shown) of a pixel transistor arranged in each of the sub-pixels, a potential for providing electrical continuity between the source and drain of the pixel transistor, and applies, to a data signal line of each of the pixel transistors, a voltage corresponding to the gradation value of the sub-pixel. 
       FIG. 3  is a diagram schematically showing a cross-section of the TFT substrate  220  taken along the line III-III in  FIG. 2 . As shown in the drawing, the TFT substrate  220  includes a glass substrate  281  as an insulating substrate, a TFT circuit layer  282  that is formed on the glass substrate  281  and in which circuits including pixel transistors  289  and the like are formed, a planarization film  283  that is formed of an insulating material on the TFT circuit layer  282 , anode electrodes  285  each of which is connected to the circuit of the TFT circuit layer  282  via a through-hole opened through the planarization film  283 , insulating banks  286  that cover edges of the anode electrodes  285  and each insulate electrodes from each other between the sub-pixels, an organic layer  300  that includes common layers such as alight emission layer, an electron injection layer, and a hole transport layer that are formed on the anode electrodes  285  and the insulating banks  286  so as to cover the entire display area  202 , a reflective layer  284  that reflects light emitted in the light emission layer, a cathode electrode  287  that is formed on the organic layer  300  so as to cover the entire display area  202 , and a sealing film  288  that blocks the entry of the air or water from the outside for preventing the deterioration of the organic layer  300 . A current controlled by the pixel transistor  289  flows through the organic layer  300  between the anode electrode  285  and the cathode electrode  287 , whereby each of the sub-pixels emits light in the light emission layer in the organic layer  300 . 
       FIG. 4  is a diagram schematically showing the stacked structure of the organic layer  300 . As shown in the drawing by way of example, the organic layer  300  formed between the anode electrode  285  and the cathode electrode  287  has a so-called tandem structure including n layers (n is plural) of light emission layers, and is composed of n layers of units  305 . The units  305  have such a structure that each of the units  305  includes a hole transport layer (HTL)  301 , a light emission layer (EML)  302 , and an electron transport layer (ETL)  303  in this order from the anode electrode  285  side, and when the unit  305  is further overlaid, a charge generation layer (CGL)  304  is interposed between the units  305 . Here, a description will be briefly given of how to emit light. Holes injected from the anode electrode  285  travel through the hole transport layer  301  and the light emission layer  302  in this order, while electrons injected from the cathode electrode  287  travel through the electron transport layer  303  and the light emission layer  302  in this order. The holes and electrons are recombined in the light emission layer  302  to form an excited state, and light emission occurs when the state transits to a ground state. A compound used for each of the hole transport layer  301 , the light emission layer  302 , the electron transport layer  303 , and the charge generation layer  304  is a well-known compound, and therefore, the description thereof is omitted. The present inventors of the invention have conceived that electrical color mixture is caused by the charge generation layer acting as a conductive layer to an adjacent pixel, and have configured an organic EL element as described below. 
       FIG. 5  is a diagram showing the organic layer  300  used in the embodiment in which the number of units is two. As shown in the drawing, the organic layer  300  is composed of a first unit  315  and a second unit  325 . The first unit  315  includes a hole transport layer  311 , a blue light emission layer  312  that emits blue light, an electron transport layer  313 , and a charge generation layer  314 . The second unit  325  includes a hole transport layer  321 , a yellow light emission layer  322  that emits yellow light, and an electron transport layer  323 . In the organic layer  300 , blue light and yellow light are simultaneously emitted, whereby white light is emitted as a whole. However, the organic layer  300  may have a configuration having other luminescent colors than these lights, or may have a configuration in which the number of units is three or more. 
       FIG. 6  is a diagram showing sub-pixels constituting the pixel  280 . As shown in the drawing, the pixel  280  is composed of four sub-pixels, an R (red) sub-pixel  331 , a G (green) sub-pixel  332 , a B (blue) sub-pixel  333 , and a W (white) sub-pixel  334 . The color filter substrate  230  includes color filters that transmit lights in wavelength ranges corresponding to the respective colors. The W lights emitted from the respective sub-pixels exit through the color filters as the corresponding R, G, B, and W lights. 
       FIG. 7  is a diagram showing a cross-section taken along the line VII-VII in  FIG. 6 .  FIG. 8  is a diagram showing a cross-section taken along the line VIII-VIII in  FIG. 6 . In these drawings, only the charge generation layer  314  of the layers included in the organic layer  300  is differently shown for the sake of description.  FIG. 7  is a diagram showing cross-sections of the W sub-pixel  334  and the G sub-pixel  332 , showing the case where light emission occurs in the blue light emission layer  312  and the yellow light emission layer  322  of the W sub-pixel  334 . In this case, a portion of electrons generated in a charge generation layer  314 A of the W sub-pixel  334  flows into the G sub-pixel  332  adjacent thereto, causing light emission (color mixture) in the G sub-pixel  332 . The W sub-pixel  334  and the G sub-pixel  332  are pixels that respectively allow lights in W and G wavelength ranges to exit, and the W and G wavelength ranges are wavelength ranges that contribute luminance out of chromaticity and luminance. Therefore, even when such electrical color mixture occurs, a change in chromaticity is limited and not much perceived by human vision. In the meantime, since the area of light emission is widened, and light emission in the G sub-pixel  332  is superimposed, current efficiency is enhanced. 
       FIG. 8  is a diagram showing cross-sections of the B sub-pixel  333  and the R sub-pixel  331 , showing the case where light emission occurs in the blue light emission layer  312  and the yellow light emission layer  322  of the B sub-pixel  333 . The charge generation layer  314  of the B sub-pixel  333  and the R sub-pixel  331  is formed of a charge generation layer  314 B thinner than the charge generation layer  314 A of the W sub-pixel  334  and the G sub-pixel  332 . For this reason, electrons generated in the charge generation layer  314 B of the B sub-pixel  333  scarcely flow into the R sub-pixel  331  adjacent thereto. Hence, electrical color mixture is less likely to occur between the B sub-pixel  333  and the R sub-pixel  331 . Since the B sub-pixel and the R sub-pixel are pixels for wavelength ranges that bear chromaticity rather than luminance, an image with higher quality can be displayed by suppressing the electrical color mixture between these pixels. 
       FIG. 9  is a diagram schematically showing the arrangement of the thick charge generation layer  314 A and the thin charge generation layer  314 B. As shown in the drawing, the charge generation layer  314 A and the charge generation layer  314 B are alternately formed in a stripe pattern in the pixel arrangement of the embodiment. Therefore, even when the charge generation layers are formed by, for example, deposition, the thin charge generation layer  314 B is formed in the entire display area, and then, the charge generation layer  314 A is formed only at portions to be formed thick additionally using a deposition mask. 
     In the embodiment as has been described above, the electrical color mixture between the B sub-pixel  333  and the R sub-pixel  331  is suppressed while the electrical color mixture between the W sub-pixel  334  and the G sub-pixel  332  is permitted to some extent. Therefore, an influence on chromaticity in vision is minimized, so that an image with high quality can be displayed. Moreover, since movement of electrons occurs between the W sub-pixel  334  and the G sub-pixel  332  so as to compensate luminance, current efficiency can be enhanced. 
       FIG. 10  is a diagram showing the arrangement of a charge generation layer  414  of an organic EL display device including three kinds of sub-pixels, an R sub-pixel  431 , a G sub-pixel  432 , and a B sub-pixel  433 , in each of pixels as a modified example of the embodiment. As shown in the drawing, the R sub-pixels, the G sub-pixels, and the B sub-pixels are respectively arranged so as to be lined up in the vertical direction in the modified example. In this case, a thin charge generation layer  414 A is formed in the R sub-pixel  431  and the B sub-pixel  433 , while a thick charge generation layer  414 B is formed in the G sub-pixel  432 . Hence, also in the modified example, the thin charge generation layer  414 A is formed in the entire display area, and then, the charge generation layer  414 B is formed only at portions to be formed thick additionally using a deposition mask. Moreover, similarly to the embodiment described above, electrical color mixture between the B sub-pixel  433  and the R sub-pixel  431  is suppressed while electrical color mixture between the G sub-pixels  432  is permitted to some extent. Therefore, an advantageous effect similar to that of the embodiment described above can be obtained. 
     In the embodiment and modified example described above, examples of the number and arrangement of sub-pixels in each pixel are shown. However, the invention is applicable even when the number and arrangement of sub-pixels are other than those of the embodiment and modified example. 
     In the embodiment and modified example described above, the organic EL display device is of top emission type. However, the organic EL display device may be of bottom emission type. 
     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.