Patent Publication Number: US-2021184179-A1

Title: Display device having a low refractive index layer and a high refractive index layer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of co-pending U.S. patent application Ser. No. 15/894,334, filed Feb. 12, 2018, which claims priority to and the benefit of Korean Patent Application No. 10-2017-0084946 filed in the Korean Intellectual Property Office on Jul. 4, 2017, the entire contents of which are herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a display device, and more particularly, to a display device having a low refractive index layer and a high refractive index layer. 
     DISCUSSION OF THE RELATED ART 
     An organic light emitting diode (OLED) display includes two electrodes and an organic emission layer interposed therebetween. Electrons are injected to the organic emission layer from one of the two electrodes and holes are injected to the organic emission layer from the other of the two electrodes. The electrons and holes are combined in the organic emission layer to generate excitons. As the generated excitons relax to a ground state from an exited state, light is emitted. 
     The organic light emitting diode (OLED) display includes a plurality of pixels including an organic light emitting diode as a self-emissive element. A plurality of transistors for driving the organic light emitting diode and at least one capacitor are formed in each pixel. The transistors generally include a switching transistor and a driving transistor. 
     A considerable amount of light emitted from the organic light emitting diode is lost as the light passes through several layers of the display. 
     SUMMARY 
     A display device includes a substrate. A first electrode is disposed on the substrate. A pixel definition layer is disposed on the substrate. A second electrode is disposed on the first electrode and the pixel definition layer. An organic emission layer is disposed between the first electrode and the second electrode. A planarization layer is disposed on the second electrode. A low refractive index layer is disposed on the planarization layer and overlaps the pixel definition layer. A high refractive index layer is disposed on the planarization layer and overlaps the second electrode. The high refractive index layer has a higher refractive index than that of the low refractive index layer. 
     The low refractive index layer may have a tapered shape. 
     A taper angle θ of the low refractive index layer may satisfy a following equation: 
     
       
         
           
             
               
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     wherein n1 is a refractive index of the low refractive index layer, n2 is a refractive index of the high refractive index layer, and asind (x) represents an angle in degrees. 
     The high refractive index layer may contact the low refractive index layer. 
     The high refractive index layer may at least partially cover the low refractive index layer. 
     A top surface of the high refractive index layer may be substantially planar. 
     A thickness of the low refractive index layer may be 4 μm or more and 8 μm or less. 
     The thickness of the low refractive index layer may be 5 μm. 
     An emission region may be separated from the low refractive index layer. 
     The emission region might not vertically overlap the low refractive index layer. 
     A horizontal distance between the emission region and the low refractive index layer may be 0.5 μm or more and 3 μm or less. 
     The horizontal distance between the emission region and the low refractive index layer may be 1.5 μm. 
     A thickness of the planarization layer may be 4 μm or more and 10 μm or less. 
     A refractive index of the planarization layer may be greater than that of the low refractive index layer, and may be smaller than that of the high refractive index layer. 
     The substrate may include a plurality of pixels, and each of the plurality of pixels may be arranged in an orthogonal matrix form or a pentile matrix form. 
     An emission region of each of the plurality of pixels may have a circular shape. 
     An emission region of each of the plurality of pixels may have a polygonal shape. 
     The display device may further include a first buffer layer disposed between the second electrode and the planarization layer. 
     The display device may further include a second buffer layer disposed between the planarization layer and the low refractive index layer, and between the planarization layer and the high refractive index layer. 
     The display device may further include a polarizer disposed on the high refractive index layer. 
     The display device may further include a cover window disposed on the high refractive index layer. 
     The display device may further include a light blocking member disposed on the low refractive index layer. 
     The high refractive index layer may include a color filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present disclosure and many of the attendant aspects thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view illustrating a display device according to an exemplary embodiment of the present invention; 
         FIG. 2  is a cross-sectional view illustrating various layers of a display device according to an exemplary embodiment of the present invention; 
         FIG. 3  is a graph illustrating a front efficiency increment with respect to a thickness of a low refractive index layer of a display device according to an exemplary embodiment of the present invention; 
         FIG. 4  is a graph illustrating a front efficiency increment with respect to a horizontal distance between a low refractive index layer and an emission region of a display device according to an exemplary embodiment of the present invention; 
         FIG. 5  is a cross-sectional view illustrating various layers of a display device according to an exemplary embodiment of the present invention; 
         FIG. 6  is a top plan view illustrating an emission region and a light-extracting region of a display device according to an exemplary embodiment of the present invention; 
         FIG. 7  is a cross-sectional view illustrating various layers of a display device according to an exemplary embodiment of the present invention; 
         FIG. 8  is a top plan view illustrating an emission region and a light-extracting region of a display device according to an exemplary embodiment of the present invention; 
         FIG. 9  is a graph illustrating light-extracting efficiency with respect to a thickness of a planarization layer according to an exemplary embodiment of the present invention; 
         FIG. 10  to  FIG. 12  are diagrams illustrating various shapes of a plurality of pixels of a display device according to an exemplary embodiment of the present invention; 
         FIG. 13  is a cross-sectional view illustrating a display device according to an exemplary embodiment of the present invention; and 
         FIG. 14  is a cross-sectional view illustrating a display device according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     In the drawings, for better understanding and ease of description, the thicknesses and shapes of some layers and areas may be exaggerated. 
     It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. 
     First, a display device according to an exemplary embodiment will be described with reference to  FIG. 1 . 
       FIG. 1  is a cross-sectional view illustrating a display device according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , the display device, according to an exemplary embodiment of the present invention includes a substrate  110 , an organic light emitting diode OLED disposed on the substrate  110 , a planarization layer  420  disposed on the organic light emitting diode OLED, a low refractive index layer  510  disposed on the planarization layer  420 , and a high refractive index layer  520  disposed on the low refractive index layer  510  and the high refractive index layer  520 . 
     The substrate  110  may be an insulating substrate made of glass, quartz, ceramic, plastic, etc., or a metal substrate made of stainless steel or the like. The substrate  110  may be flexible, stretchable, foldable, bendable, and/or rollable. As the substrate  110  may be flexible, stretchable, foldable, bendable, and/or rollable, the display device may also be flexible, stretchable, foldable, bendable, and/or rollable. 
     A buffer layer  120  may be disposed on the substrate  110 . The buffer layer  120  may be formed as a single layer of a silicon nitride (SiN x ), or as multiple layers in which a silicon nitride (SiN x ) and a silicon oxide (SiO x ) are stacked. The buffer layer  120  serves to flatten a surface while preventing undesirable materials such as impurities or moisture from permeating therethrough. The buffer layer  120  may be omitted. The buffer layer  120  may be formed to cover an entire top surface of the substrate  110 . 
     A semiconductor  135  is disposed on the buffer layer  120 . The semiconductor  135  may be made of a polycrystalline semiconductor material or an oxide semiconductor material. In addition, the semiconductor  135  includes a channel region  131  in which impurities are not doped, and contact doping regions  132  and  133  that are disposed at opposite sides of the channel region  131  and in which impurities are doped. The contact doping regions  132  and  133  include a source region  132  and a drain region  133 . The impurities used to dope the contact doping regions  132  and  133  may vary depending on a kind of the thin film transistor. 
     A gate insulating layer  140  is disposed on the semiconductor  135 . The gate insulating layer  140  may be made of an inorganic insulating material such as a silicon nitride (SiN x ) or a silicon oxide (SiO x ). 
     A gate electrode  125  is disposed on the gate insulating layer  140 . The gate electrode  125  may overlap at least some of the semiconductor  135 , and may overlap the channel region  131 . In this case, “overlap” may mean to be disposed on top of another element in a vertical direction in a cross-sectional view. 
     An interlayer insulating layer  160  is disposed on the gate electrode  125  and the gate insulating layer  140 . The interlayer insulating layer  160  may be made of the inorganic insulating material or the organic insulating material. 
     Contact holes  162  and  164  overlapping at least part of the semiconductor  135  are formed in the gate insulating layer  140  and the interlayer insulating layer  160 . The contact holes  162  and  164  respectively expose the contact doping regions  132  and  133  of the semiconductor  135 . 
     A source electrode  173  and a drain electrode  175  are disposed on the interlayer insulating layer  160 . In addition, the source electrode  173  and the drain electrode  175  are connected to the source region  132  and the drain region  133  of the semiconductor  135  through the contact holes  162  and  164 , respectively. 
     As described above, the semiconductor  135 , the gate electrode  125 , the source electrode  173 , and the drain electrode  175  comprise one thin film transistor. A structure of the thin film transistor is not limited to the aforementioned example, and may be modified to a variety of alternative structures. The organic light emitting diode display may include a switching transistor and a driving transistor, and the aforementioned thin film transistor may be the driving transistor. Although not illustrated, a switching thin film transistor may be provided. 
     A passivation layer  180  is disposed on the thin film transistor and the interayer insulating layer  160 . The passivation layer  180  serves to remove and/or flatten out steps of the aforementioned structures, thereby increasing luminous efficiency of the organic light emitting diode to be formed thereon. A contact hole  182  overlapping at least some of the drain electrode  175  is formed in the passivation layer  180 . 
     The passivation layer  180  may be formed of a polyacrylate resin, an epoxy resin, a phenolic resin, a polyamide resin, a polyimide resin, an unsaturated polyester resin, a polyphenylene resin, a polyphenylene sulfide resin, and/or benzocyclobutene (BCB). 
     The organic light emitting diode OLED is disposed on the passivation layer  180 . The organic light emitting diode OLED includes a first electrode  191 , a second electrode  270  disposed on the first electrode  191 , and an organic emission layer  370  disposed between the first electrode  191  and the second electrode  270 . 
     The first electrode  191  is disposed on the passivation layer  180 . The pixel electrode  191  may be formed of a transparent conductive material such as indium-tin oxide (ITO), indium-zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), or the like, or a reflective metal such as lithium (Li), calcium (Ca), lithium fluoride/calcium (LiF/Ca), lithium fluoride/aluminum (LiF/A), aluminum (Al), silver (Ag), magnesium (Mg), gold (Au), or the like. The first electrode  191  is electrically connected to the drain electrode  175  of the thin film transistor via the contact hole  182  formed in the passivation layer  180 , to serve as an anode of the organic light emitting diode. 
     The first electrode  191  may include first and second transparent electrodes including a transparent conductive material, and a semi-transmissive layer disposed between the first and second transparent electrodes to form a microcavity together with the second electrode  270 . For example, the first electrode  191  may be formed as multiple layers including a layer made of the transparent conductive material and a layer made of a reflective metal material. 
     A pixel definition layer  350  is disposed on an edge portion of the first electrode  191  and on the passivation layer  180 . The pixel definition layer  350  may include a resin such as a polyacrylate resin and a polyimide resin, and/or a silica-based inorganic material. 
     The organic emission layer  370  is disposed on the first electrode  191 . The organic emission layer  370  may include an emission layer, a hole-injection layer (HIL), a hole-transport layer (HTL), an electron-transport layer (ETL), and/or an electron-injection layer (EIL). 
     The organic emission layer  370  may include one of a red organic emission layer for emitting red light, a green organic emission layer for emitting green light, and a blue organic emission layer for emitting blue light. The red organic emission layer, the green organic emission layer, and the blue organic emission layer are respectively disposed at different pixels to implement a color image by a combination of differently colored pixels. 
     Alternatively, the organic emission layer  370  may have a structure in which the red organic emission layer, the green organic emission layer, and the blue organic emission layer are respectively stacked on corresponding pixels. In this case, a color image may be implemented by forming a red filter, a green filter, or a blue filter for each pixel. In another example, by forming a white organic emission layer for emitting white light at each pixel and by forming a red filter, a green filter, and a blue filter for each pixel, a color image may be implemented. When the color image is implemented by using the white organic emission layer and the color filter, a deposition mask for respectively depositing the red organic emission layer, the green organic emission layer, and the blue organic emission layer on each corresponding pixel (the red pixel, the green pixel, and the blue pixel), is not required. 
     The white organic emission layer described herein may be formed as a single organic emission layer, and may be formed as a plurality of organic emission layers stacked so that the white light may be emitted. For example, a structure for emitting white light by combining at least one yellow organic emission layer with at least one blue organic emission layer, a structure for emitting white light by combining at least one cyan organic emission layer with at least one red organic emission layer, and a structure for emitting white light by combining at least one magenta organic emission layer with at least one green organic emission layer, may be included. 
     The second electrode  270  is disposed on the organic emission layer  370  and the pixel definition layer  350 . The second electrode  270  may be made of a transparent conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), etc., or a reflective metal such as lithium (Li), calcium (Ca), lithium fluoride/calcium (LiF/Ca), lithium fluoride/aluminum (LiF/Al), aluminum (Al), silver (Ag), magnesium (Mg), gold (Au), etc. The second electrode  270  serves as a cathode of the organic light emitting diode OLED. 
     The planarization layer  420  is disposed on the second electrode  270 . A top surface of the second electrode  270  might not be flat. A portion of the second electrode  270  which overlaps the pixel definition layer  350  may protrude past other portions. This may be caused by the pixel definition layer  350  being thicker than other constituent elements. The planarization layer  420  may be formed of a transparent organic material. For example, the planarization layer  420  may be formed of a polyacrylate resin, an epoxy resin, a phenolic resin, a polyamide resin, a polyimide resin, an unsaturated polyester resin, a polyphenylene resin, a polyphenylene sulfide resin, and/or benzocyclobutene (BCB). 
     The planarization layer  420  is formed to be sufficiently thick such that a top surface thereof can be flattened. When the substrate  110  is bent to implement a flexible display device or the like, the planarization layer  420  may serve to absorb impact transmitted to elements such as the thin film transistor, the first electrode  191 , and the second electrode  270  so as to increase safety of the elements. 
     A buffer layer  410  may be further disposed between the second electrode  270  and the planarization layer  420 . The buffer layer  410  may be made of an inorganic insulating material, and may have a single layer or multiple layer structure. For example, the buffer layer  410  may be made of silicon oxynitride (SiON). The buffer layer  410  may serve to protect the organic light emitting diode OLED. The buffer layer  410  may be omitted in some cases. 
     The low refractive index layer  510  is disposed on the planarization layer  420  to overlap the pixel definition layer  350 . The low refractive index layer  510  may overlap most regions of the pixel definition layer  350  other than a portion of an edge thereof. The low refractive index layer  510  is illustrated to not overlap the first electrode  191  at all, but may overlap a portion of the edge of the first electrode  191  in some cases. 
     Light is emitted in a region where the organic emission layer  370  is in contact with the first electrode  191  and the second electrode  270 . Accordingly, a region where all of the first electrode  191 , the organic emission layer  370 , and the second electrode  270  are overlapped may be regarded as an emission region ER. The emission region ER where light generated from the organic emission layer  370  is emitted may be separated from the low refractive index layer  510 . For example, the emission region ER might not overlap the low refractive index layer  510 . A distance between the emission region ER and the low refractive index layer  510  and a thickness of the low refractive index layer  510  etc. will be further described later. 
     A side surface of the low refractive index layer  510  may be inclined with respect to the planarization layer  420 . For example, the low refractive index layer  510  may have a tapered shape at ends thereof. A taper angle of the low refractive index layer  510  will be further described later. 
     The high refractive index layer  520  is disposed on the planarization layer  420  to overlap the second electrode  270 . The high refractive index layer  520  may also overlap the pixel definition layer  350 , and may be disposed on the low refractive index layer  510  to cover the low refractive index layer  510 . The high refractive index layer  520  may be formed to cover an entire top surface of the substrate  110 . 
     The high refractive index layer  520  may have a higher refractive index than the low refractive index layer  510 . 
     The high refractive index layer  520  may be formed of a transparent organic material 
     The high refractive index layer  520  may be formed to be sufficiently thick such that a top surface thereof is flattened (e.g. planar). The high refractive index layer  520  may be made of a material having a refractive index that is higher than a refractive index of a material that the low refractive index layer  510  is made of. The high refractive index layer  520  may contact the low refractive index layer  510 . When the light generated in the emission region ER is introduced into the low refractive index layer  510  through the high refractive index layer  520 , the light is totally reflected toward a front surface thereof. 
     Hereinafter, a taper angle of the low refractive index layer  510  for guiding the total reflection will be described with reference to  FIG. 2 . 
       FIG. 2  is a cross-sectional view illustrating some layers of a display device according to an exemplary embodiment of the present invention.  FIG. 2  illustrates the buffer layer  430 , the low refractive index layer  510 , and the high refractive index layer  520 , and a light path is indicated by an arrow. 
     Some of the light generated in the organic emission layer  370  may be emitted toward a front side of a screen, e.g., in a direction perpendicular to the substrate  110 . Some of the light passes at an oblique angle relative to the substrate  110 , and is introduced into the low refractive index layer  510  through the high refractive index layer  520 . When passing from a medium with a high refractive index to a medium with a low refractive index, the light may be totally reflected at an interface therebetween, which is called total reflection in a case where an incidence angle is greater than a critical angle. A taper angle (θ) of the low refractive index layer  510  may be adjusted by using Equation 1 such that light introduced into the low refractive index layer  510  through the high refractive index layer  520  may be totally reflected. 
     
       
         
           
             
               
                 
                   
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     (n1: a refractive index of the low refractive index layer, n2: a refractive index of the high refractive index layer, θ: taper angle of the low refractive index layer with respect to a bottom horizontal surface of the low refractive index layer) 
     For example, the refractive index of the low refractive index layer  510  may be 1.5, and the refractive index of the high refractive index layer  520  may be 1.65. In this case, the taper angle (θ) of the low refractive index layer  510  may be 65.38° (asind (1.5/1.65)) or more, and 90° or less (where (asind x) represents an angle in degrees). 
     Here, an amount of light to be lost may be reduced by allowing the light introduced into the low refractive index layer  510  through the high refractive index layer  520  to be totally reflected and to be emitted toward the front side of the screen, thereby increasing the transmittance. 
     Hereinafter, a thickness of the low refractive index layer  510  and a distance between the emission region ER and the low refractive index layer  510  will be described with reference to  FIG. 3  and  FIG. 4 . 
       FIG. 3  is a graph illustrating a front efficiency increment with respect to a thickness of a low refractive index layer of a display device according to an exemplary embodiment of the present disclosure. The front efficiency increment indicates an increment in an amount of light that is emitted toward the front side of the screen.  FIG. 4  is a graph illustrating a front efficiency increment with respect to a horizontal distance between a low refractive index layer and an emission region of a display device according to an exemplary embodiment of the present disclosure. 
     As shown in  FIG. 3 , as a thickness TH of the low refractive index layer  510  increases, the front efficiency increment tends to gradually increase and then decrease again at a certain point. Each of the red light, the green light, and the blue light have different points where the front efficiency increment is a maximum. For white light, it is seen that when the thickness TH of the low refractive index layer  510  is about 5 μm, the front efficiency is increased by 40% to a maximum. In addition, it is seen that when the thickness TH of the low refractive index layer  510  is about 4 μm or more and about 8 μm or less, the front efficiency is increased by about 30%. Accordingly, the thickness TH of the low refractive index layer  510  may preferably be about 4 μm or more and about 8 μm or less. Further, the thickness TH of the low refractive index layer  510  may more preferably be about 5 μm. 
     As shown in  FIG. 4 , as a horizontal distance SC between the emission region ER and the low refractive index layer  510  is larger, the front efficiency increment tends to gradually increase and then decrease again at a certain point. The emission region ER and the low refractive index layer  510  are horizontally and vertically separated from each other, and the horizontal distance SC indicates a distance between the emission region ER and the low refractive index layer  510  when viewed from a direction perpendicular to the top surface of the substrate  110 . Each of the red light, the green light, and the blue light have different points where the front efficiency increment is a maximum. For white light, it is seen that when the horizontal distance SC between the emission region ER and the low refractive index layer  510  is about 1.5 μm, the front efficiency is increased by 40% to a maximum. In addition, it is seen that when the horizontal distance SC between the emission region ER and the low refractive index layer  510  is about 0.5 μm or more and about 3 μm or less, the front efficiency is increased by about 30%. Accordingly, the horizontal distance SC between the emission region ER and the low refractive index layer  510  may preferably be about 0.5 μm or more and about 3 μm or less 
     Further, the horizontal distance SC between the emission region ER and the low refractive index layer  510  may preferably be about 1.5 μm. 
     A buffer layer  430  may be further disposed between the planarization layer  420  and the low refractive index layer  510 . In addition, the buffer layer  430  may also be disposed between the planarization layer  420  and the high refractive index layer  520 . For example, the buffer layer  430  may be entirely disposed on the planarization layer  420 . 
     The buffer layer  430  may be made of an inorganic insulating material, and may have a single layer or a multiple layer structure. For example, the buffer layer  430  may be made of silicon nitride (SiN x ). The buffer layer  430  may serve to prevent penetration of unnecessary components such as oxygen and moisture therethrough. 
     A polarizer  610  and a cover window  620  may be disposed on the high refractive index layer  520 . The polarizer  610  may be disposed between the high refractive index layer  520  and the cover window  620 . However, the present invention is not limited thereto, and positions of the polarizer  610  and the cover window  620  may be changed. An additional layer may be provided, and some of the aforementioned layers may be omitted. 
     The cover window  620  may serve to protect the display device from external interference. The cover window  620  may be formed of a single layer or multiple layers. 
     Hereinafter, a thickness of the planarization layer  420  will be described with reference to  FIG. 5  to  FIG. 9 . 
       FIG. 5  is a cross-sectional view illustrating various layers of a display device according to an exemplary embodiment of the present invention, and  FIG. 6  is a top plan view illustrating an emission region and a light-extracting region of a display device according to an exemplary embodiment of the present invention.  FIG. 5  and  FIG. 6  illustrate a case where a thickness To of the planarization layer is a first thickness T 1 .  FIG. 7  is a cross-sectional view illustrating various layers of a display device according to an exemplary embodiment of the present invention, and  FIG. 8  is a top plan view illustrating an emission region and a light-extracting region of a display device according to an exemplary embodiment of the present invention.  FIG. 7  and  FIG. 8  illustrate a case where the thickness To of the planarization layer is a first thickness T 2 . The first thickness is different from the second thickness.  FIG. 9  is a graph illustrating light-extracting efficiency depending on a thickness of a planarization layer. 
     As shown in  FIG. 5  and  FIG. 7 , light extraction may be performed by allowing the light emitted from the organic light emitting diode OLED to be introduced into the low refractive index layer  510  through the high refractive index layer  520 , and to be totally reflected toward a front side of the screen.  FIG. 6  and  FIG. 8  illustrate a light-extracting region XR where light may be extracted by a difference between refractive indexes of the high refractive index layer  520  and the low refractive index layer  510 . The light-extracting region XR is disposed inside the emission region ER. 
     In  FIG. 5 , the thickness To of the planarization layer  420  is the first thickness T. In  FIG. 7 , the thickness To of the planarization layer  420  is the second thickness T 2 , and the second thickness T 2  is thicker than the first thickness T 1 . Referring to  FIG. 5  to  FIG. 8 , it is seen that the light-extracting region XR is varied depending on the thickness To of the planarization layer  420 . Accordingly, a change in the light-extracting efficiency may be made depending on the change in the thickness of the planarization layer  420 . 
     Referring to  FIG. 9 , it is seen that when the thickness of the planarization layer  420  is about 4 μm or more and about 10 μm or less, light-extracting efficiency is about 10% or more and 40% or less. Accordingly, the planarization layer  420  may have a thickness that is in a range of about 4 μm or more and about 10 μm or less. For example, the planarization layer  420  may have a thickness that is in a range of about 7 μm or more and about 8 μm or less. 
     In addition, the refractive index of the planarization layer  420  is greater than that of the low refractive index layer  510 , and is smaller than that of the high refractive index layer  520 . 
     A display device according to an exemplary embodiment of the present invention may include a plurality of pixels, and the structure of one pixel has been described. Hereinafter, a planar shape and arrangement of the pixels will be described with reference to  FIG. 10  to  FIG. 12 . 
       FIG. 10  to  FIG. 12  illustrate various disposal shapes of a plurality of pixels of a display device according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 10 , the pixels may be arranged in a pentile matrix form. The pixels may include a red emission region ERr, a green emission region ERg, and a blue emission region ERb. Each of the emission regions ERr, ERg, and ERb may be formed to have a polygonal shape such as a substantially quadrangular or octagonal shape. 
     The red emission region ERr and the green emission region ERg may be arranged alternately in a diagonal direction, and the blue emission region ERb and the green emission region ERg may be arranged alternately in the diagonal direction. The red emission region ERr, the green emission region ERg, and the blue emission region ERb may be respectively disposed in different pixels, and a color image may be implemented by a combination thereof. 
     The low refractive index layer  510  may be formed to surround the red emission region ERr, the green emission region ERg, and the blue emission region ERb. The low refractive index layer  510  might not overlap the red emission region ERr, the green emission region ERg, or the blue emission region ERb. 
     The shape and arrangement of the pixels is not limited thereto. For example, as shown in  FIG. 11  and  FIG. 12 , the pixels may be disposed in a matrix form along a row direction and a column direction. 
     As shown in  FIG. 11 , emission regions ER of the pixels may have a quadrangular shape, and all of them may have a same size. Alternatively, as shown in  FIG. 12 , the emission regions ER of the pixels may have a circular shape. 
     Hereinafter, a display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 13 . 
     Since the display device shown in  FIG. 13  is substantially the same as the display device shown in  FIG. 1 , a description of similar features will be omitted and it may be assumed that where a feature of  FIG. 13  is not described, that feature may be similar to or identical to a corresponding feature of  FIG. 1 . The arrangement of  FIG. 13  is different from the aforementioned exemplary embodiment in that a light blocking member is further disposed on the low refractive index layer. 
       FIG. 13  is a cross-sectional view illustrating a display device according to an exemplary embodiment of the present invention. In  FIG. 13 , some constituent elements such as a substrate, a thin film transistor, and the like are omitted. 
     As shown in  FIG. 13 , similar to the aforementioned exemplary embodiment, the display device according to an exemplary embodiment of the present invention includes a substrate, a first electrode  191 , an organic emission layer  370 , and a second electrode  270  disposed on the substrate, a planarization layer  420  disposed on the second electrode  270 , and a low refractive index layer  510  and a high refractive index layer  520  disposed on the planarization layer  420 . 
     The organic emission layer  370  may include a red organic emission layer  370 R, a green organic emission layer  370 G, and a blue organic emission layer  370 B. 
     The display device may further include a light blocking member  530  disposed on the low refractive index layer  510 . The light blocking member  530  is disposed between adjacent emission regions. The light blocking member  530  may overlap a region between the red organic emission layer  370 R and the green organic emission layer  370 G, and may overlap a region between the green organic emission layer  370 G and the blue organic emission layer  370 B. The light blocking member  530  may overlap the low refractive index layer  510  and the pixel definition layer  350 . 
     The light blocking member  530  includes a light-blocking material, and serves to prevent external light from being reflected and recognized. 
     Hereinafter, a display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 14 . 
     Since the display device shown in  FIG. 14  is substantially the same as the display device shown in  FIG. 1 , a description of similar features will be omitted and it may be assumed that where a feature of  FIG. 14  is not described, that feature may be similar to or identical to a corresponding feature of  FIG. 1 . The arrangement of  FIG. 14  is different from the aforementioned exemplary embodiment in that the high refractive index layer includes a color filter. 
       FIG. 14  is a cross-sectional view illustrating a display device according to an exemplary embodiment of the present invention. In  FIG. 14 , some constituent elements such as a substrate, a thin film transistor, and the like are omitted. 
     As shown in  FIG. 14 , similar to the aforementioned exemplary embodiment, the display device includes a substrate (not illustrated), a first electrode  191 , an organic emission layer  370 , and a second electrode  270  disposed on the substrate, a planarization layer  420  disposed on the second electrode  270 , and a low refractive index layer  510  and a high refractive index layer  520  disposed on the planarization layer  420 . 
     In the present exemplary embodiment, the high refractive index layer  520  may include color filters  230 R,  230 G, and  230 B. The color filters  230 R,  230 G, and  230 B may include a red to filter  230 R, a green filter  230 G, and a blue filter  230 B. The red filter  230 R may overlap the red organic emission layer  370 R, the green filter  230 G may overlap the green organic emission layer  370 G, the blue filter  230 B may overlap the blue organic emission layer  370 B. 
     The light blocking member  530  may be disposed between the red filter  230 R and the green filter  230 G, and may be disposed between the green filter  2300  and the blue filter  230 B. 
     The polarizer may be omitted by further including the color filters  230 R,  230 G, and  230 B. Light loss occurs while the light passes through the polarizer. However, according to exemplary embodiments of the present invention, the transmittance may be further increased by omitting the polarizer. 
     Exemplary embodiments described herein are illustrative, and many variations can be introduced without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.