Patent Publication Number: US-9837638-B2

Title: Organic light-emitting diode display and method of manufacturing the same having light-blocking portions of black matrix with differing light transmittances

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/691,343, filed Apr. 20, 2015, now U.S. Pat. No. 9,502,485, issued Nov. 22, 2016, which claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2014-0178704, filed on Dec. 11, 2014, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Field 
     The described technology generally relates to an organic light-emitting diode display and a method of manufacturing the same. 
     Description of the Related Technology 
     An organic light-emitting diode (OLED) display includes a matrix of OLEDs each including hole injection electrodes, electron injection electrodes, and organic emission layers formed between the hole injection electrodes and the electron injection electrodes. Holes injected from the hole injection electrodes and electrons injected from the electron injection electrodes combine in the organic emission layers and generate excitons. Thus, light is generated as the excitons drop from an excited state to a ground state. 
     Since a separate light source is unnecessary, the OLED display can be driven at a low voltage and be configured to be lightweight and thin. Due to their excellent viewing angles, contrasts, response times, and other favorable characteristics, OLED displays are widely used in personal portable devices, such as MP3 players and mobile phones, TVs, etc. 
     Much research has been conducted to develop the OLED display for flexible applications, for example, a foldable or rollable display. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     One inventive aspect relates to an OLED display that is flexible and has improved visibility and a method of manufacturing the same so as to solve the above problems. 
     Another aspect is an OLED display that includes a substrate including an emission area and a non-emission area; a pixel electrode formed in the emission area of the substrate; an intermediate layer formed on the pixel electrode and including an organic emission layer; an opposite electrode formed in the emission area and the non-emission area of the substrate and covering the intermediate layer; and a black matrix including a first light-blocking unit in an area corresponding to the non-emission area and a second light-blocking unit in an area corresponding to at least the emission area and having a greater light transmittance than the first light-blocking unit, on the opposite electrode. 
     A visible light transmittance of the first light-blocking unit can be about 0.2% or less and a visible light transmittance of the second light-blocking unit can be about 40% to about 70%. 
     The first light-blocking unit can have a first thickness and the second light-blocking unit can have a second thickness, the second thickness can be smaller than the first thickness. 
     The first light-blocking unit and the second light-blocking unit can include a substantially identical material. 
     The first thickness can be about 0.8 μm or more, and the second thickness can be about 0.1 μm to about 0.5 μm. 
     The first and second light-blocking units can have a substantially identical third thickness. 
     The black matrix can include a resin including black pigments, and a density of black pigments in the first light-blocking unit can be greater than a density of black pigments in the second light-blocking unit. 
     The third thickness can be about 0.8 μm or more. 
     The OLED display can further include an encapsulating substrate that faces the substrate. The black matrix can be on a surface of the encapsulating substrate, the surface facing the substrate. 
     The OLED display can further include a thin film encapsulating layer between the opposite electrode and the black matrix. 
     Another aspect is a method of manufacturing an OLED display that includes forming a pixel electrode in an emission area of a substrate including the emission area and a non-emission area; forming an intermediate layer including an organic emission layer on the pixel electrode; forming an opposite electrode in the emission area and the non-emission area of the substrate to cover the intermediate layer; and forming a black matrix including a first light-blocking unit in an area corresponding to the non-emission area and a second light-blocking unit in an area corresponding to at least the emission area and having a greater light transmittance than the first light-blocking unit, on the opposite electrode. 
     A visible light transmittance of the first light-blocking unit can be about 0.2% or less and a visible light transmittance of the second light-blocking unit can be about 40% to about 70%. 
     The forming of the black matrix can include forming a light-blocking material to a first thickness in the non-emission area and the emission area on the opposite electrode; 
     irradiating light onto the non-emission area by using a mask including a hole corresponding to the non-emission area; and forming the second light-blocking unit to a second thickness by developing the light-blocking material and removing a portion of the light-blocking material formed in the emission area. 
     The first thickness can be about 0.8 μm or more, and the second thickness can be about 0.1 μm to about 0.5 μm. 
     The forming of the black matrix can include forming the second light-blocking unit to a fifth thickness in the emission area and the non-emission area; and forming the first light-blocking unit to a fourth thickness in the non-emission area of the second light-blocking unit. The fifth thickness can be about 0.1 μm to about 0.5 μm, and a sum of the fourth thickness and the fifth thickness can be about 0.8 μm or more. 
     The forming of the black matrix can include forming the first light-blocking unit to a third thickness in the non-emission area; and forming the second light-blocking unit to the third thickness in the emission area. 
     The first light-blocking unit can include a resin including black pigments, and the second light-blocking unit can include a resin including black pigments that have a lower density than the black pigments of the first light-blocking unit. 
     The third thickness can be about 0.8 μm or more. 
     The method can further include forming an encapsulating substrate to face the substrate; forming the black matrix on a surface of the encapsulating substrate, the surface facing the substrate; and aligning the substrate and the encapsulating substrate. 
     The method can further include, after the forming of the opposite electrode, forming a thin film encapsulating layer on the opposite electrode. 
     Another aspect is an organic light-emitting diode (OLED) display, comprising a substrate having an emission area and a non-emission area, a pixel electrode formed in the emission area, an intermediate layer formed over the pixel electrode and comprising an organic emission layer, an opposite electrode formed in the emission and non-emission areas and at least partially covering the intermediate layer; and a black matrix formed over the opposite electrode and comprising i) a first light-blocking portion formed in the non-emission area and ii) a second light-blocking portion formed in the emission area and having light transmittance greater than that of the first light-blocking portion. 
     In the above display, the light transmittance of the first light-blocking portion is about 0.2% or less, wherein the light transmittance of the second light-blocking portion is about 40% to about 70%. 
     In the above display, the first light-blocking portion has a first thickness and the second light-blocking portion has a second thickness less than the first thickness. 
     In the above display, the first and second light-blocking portions are formed of the same material. 
     In the above display, the first thickness is about 0.8 μm or more, wherein the second thickness is about 0.1 μm to about 0.5 μm. 
     In the above display, the first and second light-blocking portions have substantially the same thickness. 
     In the above display, the black matrix is formed of a resin comprising black pigments, wherein the density of the black pigments in the first light-blocking portion is greater than the density of black pigments in the second light-blocking portion. 
     In the above display, the thickness of the first and second light-blocking portions is about 0.8 μm or more. 
     The above OLED display further comprises an encapsulating substrate facing the substrate, wherein the black matrix is formed over a surface of the encapsulating substrate, and wherein the surface faces the substrate. 
     In the above display, the opposite electrode has concave portions facing away from the substrate, wherein the first light-blocking portions are substantially rectangular and formed over the concave portions. 
     Another aspect is a method of manufacturing an OLED display, the method comprising providing a substrate having an emission area and a non-emission area, forming a pixel electrode in the emission area, forming an intermediate layer comprising an organic emission layer over the pixel electrode, forming an opposite electrode in the emission and non-emission areas so as to at least partially cover the intermediate layer, and forming a black matrix over the opposite electrode and comprising i) a first light-blocking portion over the non-emission area and ii) a second light-blocking portion formed over at least the emission area and having light transmittance greater than that of the first light-blocking portion. 
     In the above method, the light transmittance of the first light-blocking portion is about 0.2% or less, wherein the light transmittance of the second light-blocking portion is about 40% to about 70%. 
     In the above method, the forming of the black matrix comprises providing a light-blocking material having a first thickness in the non-emission area and the emission area over the opposite electrode, irradiating light onto the non-emission area through a mask having at least one hole corresponding to the non-emission area, developing the light-blocking material, and removing a portion of the light-blocking material formed in the emission area so as to form the second light-blocking portion having a second thickness. 
     In the above method, the first thickness is about 0.8 μm or more, wherein the second thickness is about 0.1 μm to about 0.5 μm. 
     In the above method, the forming of the black matrix comprises forming the first light-blocking portion having a third thickness in the non-emission area and forming the second light-blocking portion having the third thickness in the emission area. 
     In the above method, the first light-blocking portion is formed of a resin comprising black pigments, wherein the second light-blocking portion is formed of a resin comprising black pigments having a density less than that of the black pigments of the first light-blocking portion. 
     In the above method, the third thickness is about 0.8 μm or more. 
     In the above method, the forming of the black matrix comprises forming the first light-blocking portion having a fourth thickness in the non-emission area of the second light-blocking portion, forming the second light-blocking portion having a fifth thickness in the emission and non-emission areas, wherein the fifth thickness is about 0.1 μm to about 0.5 μm, and wherein the sum of the fourth and fifth thicknesses is about 0.8 μm or more. 
     The above method further comprises forming an encapsulating substrate having a surface facing the substrate, forming the black matrix over the surface of the encapsulating substrate, and aligning the substrate and the encapsulating substrate. 
     In the above method, the opposite electrode has concave portions facing away from the substrate, and wherein the first light-blocking portions are substantially rectangular and formed over the concave portions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view schematically illustrating an OLED display according to an exemplary embodiment. 
         FIGS. 2A to 2D  are cross-sectional views sequentially illustrating a method of manufacturing the OLED display of  FIG. 1 . 
         FIG. 3  is a cross-sectional view schematically illustrating an OLED display according to an exemplary embodiment. 
         FIGS. 4A and 4B  are cross-sectional views sequentially illustrating a part of a method of manufacturing the OLED display of  FIG. 3 . 
         FIG. 5  is a cross-sectional view schematically illustrating an OLED display according to an exemplary embodiment. 
         FIGS. 6A and 6B  are cross-sectional views sequentially illustrating a portion of a method of manufacturing the OLED display of  FIG. 5 . 
         FIG. 7  is a cross-sectional view schematically illustrating an OLED display according to an exemplary embodiment. 
         FIG. 8  is a cross-sectional view illustrating a portion of a method of manufacturing the OLED display of  FIG. 7 . 
         FIG. 9  is a graph illustrating an external light reflectance and a transmittance of light emitted from an intermediate layer, versus wavelengths, of the OLED display of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS 
     Although typical OLED displays (not necessarily prior art) include a circular polarizing film to improve visibility thereof, the circular polarizing film has a thickness of about 100 μm or more, and thus, these OLED displays are not flexible. 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present exemplary embodiments can have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the exemplary embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed item. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     It will be understood that although the terms “first”, “second”, etc. can be used herein to describe various components, these components should not be limited by these terms. These components are only used to distinguish one component from another. 
     As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It will be further understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components. 
     It will be understood that when a layer, region, or component is referred to as being “formed on,” another layer, region, or component, it can be directly or indirectly formed on the other layer, region, or component. That is, for example, intervening layers, regions, or components can be present. 
     Sizes of elements in the drawings can be exaggerated for convenience of explanation. In other words, since sizes and thicknesses of components in the drawings are arbitrarily illustrated for convenience of explanation, the following embodiments are not limited thereto. In this disclosure, the term “substantially” includes the meanings of completely, almost completely or to any significant degree under some applications and in accordance with those skilled in the art. Moreover, “formed on” can also mean “formed over.” The term “connected” can include an electrical connection. 
       FIG. 1  is a cross-sectional view schematically illustrating an OLED display  1  according to an exemplary embodiment. 
     Referring to  FIG. 1 , the OLED display  1  according to an exemplary embodiment includes a substrate  110  having an emission area EA and a non-emission area NA, and pixel electrodes  121   a ,  121   b , and  121   c  formed in the emission area EA. the OLED display  1  also includes intermediate layers  123   a ,  123   b , and  123   c  including organic emission layers and formed on the pixel electrodes  121   a ,  121   b , and  121   c , an opposite electrode  125  formed in the emission area EA and the non-emission area NA to cover the intermediate layers  123   a ,  123   b , and  123   c , and a black matrix  140  including a first light-blocking unit or first light-blocking portion  141  formed in an area corresponding to the non-emission area NA and a second light-blocking unit or second light-blocking portion  142  formed in an area corresponding to at least the emission area EA and having light transmittance greater than that of the first light-blocking unit  141 , on the opposite electrode  125 . 
     The substrate  110  can include a thin film transistor (TFT) array substrate formed by forming driving devices such as TFTs (not shown) on a base substrate that can be a flexible substrate. For example, the base substrate is formed of plastic with excellent heat-resistance and durability such as polyimide, polyethylene terephthalate (PET), polycarbonate, polyethylene naphtalate, polyacrylate (PAR), and polyetherimide. 
     The substrate  110  includes the emission area EA and the non-emission area NA. The emission area EA can include sub-pixel areas that emit different colors of light. For example, the emission area EA includes, but is not limited to, a red sub-pixel, a green sub-pixel, and a blue sub-pixel that respectively emit red light, green light, and blue light. 
     Each of the pixel electrodes  121   a ,  121   b , and  121   c  can be a reflection electrode that includes a reflection layer. For example, the reflection layer is formed of at least one of silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), and chrome (Cr). A transparent or semi-transparent electrode layer can be additionally formed on the reflection layer from one selected from the group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), indium gallium oxide (IGO), and aluminum zinc oxide (AZO). For example, the pixel electrodes  121   a ,  121   b , and  121   c  is formed as a 3-layer structure of ITO/Ag/ITO. 
     Both edges of each of the pixel electrodes  121   a ,  121   b , and  121   c  can be covered by a pixel defining layer (PDL)  122  that can define the emission area EA. 
     The intermediate layers  123   a ,  123   b , and  123   c  can be formed in areas of the pixel electrodes  121   a ,  121   b , and  121   c  which are exposed by the PDL  122 . Each of the intermediate layers  123   a ,  123   b , and  123   c  includes an organic emission layer and can further include at least one selected from a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), and an electron injection layer (EIL). However, the embodiments are not limited thereto, and each of the intermediate layers  123   a ,  123   b , and  123   c  includes an organic emission layer and can further include other various functional layers. 
     When an OLED is a full color OLED, the organic emission layer can be patterned to form a red emission layer, a green emission layer, and a blue emission layer according to the red sub-pixel, the green sub-pixel, and the blue sub-pixel. 
     The organic emission layer can have a multi-layer structure formed by stacking the red emission layer, the green emission layer, and the blue emission layer so that white light is emitted, or a single layer structure formed of a red light-emitting material, a green light-emitting material, and a blue light-emitting material. The OLED including the above-described organic emission layer can emit full colors by further including a red color filter, a green color filter, and a blue color filter. 
     The opposite electrode  125  can be formed over both the emission area EA and the non-emission area NA, and can include a semi-transparent electrode that transmits some rays of light and reflects other rays of light. 
     The opposite electrode  125  can be formed of a material having a product of a refractive index and an extinction ratio equal to 10 or less in a visible light area, a low absorption rate, and a high reflectance. For example, the opposite electrode  125  is formed of at least one selected from Ag, Al, ytterbium (Yb), Ti, Mg, Ni, lithium (Li), calcium (Ca), copper (Cu), LiF/Ca, LiF/Al, MgAg, and CaAg. The at least one selected material can be formed as a thin film having a thickness of few to several nm so that the thin film has a certain degree of transmittance. 
     The opposite electrode  125  can be formed as a semi-transparent electrode so that the pixel electrodes  121   a ,  121   b , and  121   c  and the opposite electrode  125  form a microcavity. That is, some light rays emitted from the intermediate layers  123   a ,  123   b , and  123   c  formed between the pixel electrodes  121   a ,  121   b , and  121   c  and the opposite electrode  125  can travel back and forth between the pixel electrodes  121   a ,  121   b , and  121   c  and the opposite electrode  125 , and light rays having a certain wavelength that satisfies a constructive interference condition can be amplified during the travelling and be emitted toward the opposite electrode  125 . 
     The intermediate layers  123   a ,  123   b , and  123   c  can include a resonance length adjusting layer that is formed above and/or under the organic emission layers and can adjust a distance between the pixel electrodes  121   a ,  121   b , and  121   c  and the opposite electrode  125  according to a wavelength of light rays emitted from the organic emission layers. 
     A thin film encapsulating layer  130  can be formed between the opposite electrode  125  and the black matrix  140 . The thin film encapsulating layer  130  can include at least one inorganic layer and at least one organic layer. The total thickness of the thin film encapsulating layer  130  can be about 2 μm to about 20 μm. The above range can provide an optimum balance between an efficient performance of an encapsulation function and the flexibility of an OLED display. However, depending on embodiments, the total thickness can be less than about 2 μm or greater than about 20 μm. 
     The at least one inorganic layer included in the thin film encapsulating layer  130  can be formed of a metal oxide, a metal nitride, a metal carbide, or a combination thereof, for example, Al oxide, silicon oxide, or silicon nitride. The at least one inorganic layer can block external moisture and/or oxygen from penetrating through the intermediate layers  123   a ,  123   b , and  123   c.    
     The at least one organic layer included in the thin film encapsulating layer  130  can be formed of a polymer organic compound including any one selected from epoxy, acrylate, and urethane acrylate. The at least one organic layer can reduce internal stress of the inorganic layer and compensate for defects of and planarize the inorganic layer. 
     In the OLED display  1  according to an exemplary embodiment, a base substrate can be a flexible substrate and the thin film encapsulating layer  130  can be included as an encapsulating unit, and thus, a flexible OLED display  1  can be easily manufactured. 
     The black matrix  140  can be formed on the thin film encapsulating layer  130 . The black matrix  140  can include the first light-blocking unit  141  in the non-emission area NA and the second light-blocking unit  142  in the emission area EA. 
     The black matrix  140  can block external light reflection so that visibility of the OLED display  1  is improved. According to an exemplary embodiment, a visible light transmittance (or light transmittance) of the first light-blocking unit  141  can be about 0.2% or less and a visible light transmittance (or light transmittance) of the second light-blocking unit  142  can be about 40% to about 70%. 
     When the visible light transmittance of the first light-blocking unit  141  exceeds about 0.2%, the effect of the external light reflection can be decreased. That is, since the first light-blocking unit  141  is located in the non-emission area NA, the visible light transmittance can be minimized so that external light reflection is efficiently prevented. However, depending on embodiments, the visible light transmittance of the first light-blocking unit  141  can be greater than about 0.2%. 
     That is, since the second light-blocking unit  142  is formed on the emission area EA, light rays emitted from the intermediate layers  123   a ,  123   b , and  123   c  can pass through the second light-blocking unit  142  and travel to the environment. The second light-blocking unit  142  can have greater visible light transmittance than that of the first light-blocking unit  141 , for example, a visible light transmittance of about 40% or more. The above range can provide an optimum balance between light extraction efficiency and an external light reflection prevention effect of the emission area EA. However, depending on embodiments, the visible light transmittance of the second light-blocking unit  142  can be less than about 40% or greater than about 70%. 
     According to an exemplary embodiment, the first light-blocking unit  141  and the second light-blocking unit  142  can include a substantially identical material, for example, a photosensitive resin including black pigments. The first and second light-blocking units  141  and  142  can have different thicknesses and thus have different visible light transmittances. That is, the first light-blocking unit  141  can have a first thickness t 1  and the second light-blocking unit  142  can have a second thickness t 2  that is less than the first thickness t 1 . 
     According to an exemplary embodiment, the first thickness t 1  can be about 0.8 μm or more and the second thickness t 2  can be about 0.1 μm to about 0.5 μm. As described above, the first light-blocking unit  141  having the first thickness t 1  can have a visible light transmittance (or light transmittance) of about 0.2% or less, and the second light-blocking unit  142  having the second thickness t 2  can have a visible light transmittance (or light transmittance) of about 40% to about 70%. However, depending on embodiments, the first thickness t 1  can be greater than about 0.8 μm and the second thickness t 2  can be less than about 0.1 μm or greater than about 0.5 μm. 
     According to an exemplary embodiment, the first light-blocking unit  141  and the second light-blocking unit  142  can be formed in one body. A step can be formed due to the difference between respective thicknesses of the first light-blocking unit  141  and the second light-blocking unit  142 . The first light-blocking unit  141  and the second light-blocking unit  142  can be easily manufactured according to a masking process, which will be described later. 
     An overcoat film  150  can be formed on the black matrix  140 , and a window  160  can be formed on the overcoat film  150 . According to an exemplary embodiment, the OLED display  1  efficiently prevents external light reflection without using a polarizer that is generally used in this regard and also can be easily manufactured to be flexible. 
       FIGS. 2A to 2D  are cross-sectional views sequentially illustrating a method of manufacturing the OLED display  1  of  FIG. 1 . 
     Referring to  FIG. 2A , the method includes forming the pixel electrodes  121   a ,  121   b , and  121   c  on the emission area EA of the substrate  110  and forming the PDL  122  that covers both edges of each of the pixel electrodes  121   a ,  121   b , and  121   c.    
     Each of the pixel electrodes  121   a ,  121   b , and  121   c  can be a reflection electrode that includes a reflection layer. For example, the reflection layer is formed of at least one of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, and Cr. On the reflection layer, a transparent or semi-transparent electrode layer that is formed by one of ITO, IZO, ZnO, In 2 O 3 , IGO, and AZO can be additionally formed. For example, the pixel electrodes  121   a ,  121   b , and  121   c  is formed as a 3-layer structure of ITO/Ag/ITO. 
     The pixel electrodes  121   a ,  121   b , and  121   c  can be formed as islands on sub-pixels corresponding thereto. 
     Referring to  FIG. 2B , the method of manufacturing the OLED display  1  can include forming the intermediate layers  123   a ,  123   b , and  123   c  that include organic emission layers on the pixel electrodes  121   a ,  121   b , and  121   c , respectively, after forming the PDL  122 . The method can also include forming the opposite electrode  125  in the emission area EA and the non-emission area NA to cover the intermediate layers  123   a ,  123   b , and  123   c , and forming the thin film encapsulating layer  130  on the opposite electrode  125 . 
     Each of the intermediate layers  123   a ,  123   b , and  123   c  includes an organic emission layer and can further include at least one selected from a HIL, a HTL, an ETL, and an EIL. The organic emission layers can be patterned as a red emission layer, a green emission layer, and a blue emission layer according to the red sub-pixel, the green sub-pixel, and the blue sub-pixel. 
     The opposite electrode  125  can be formed in common over the emission area EA and the non-emission area NA, and can be a semi-transparent electrode that transmits some rays of light and reflects the other rays of light. For example, the opposite electrode  125  is formed of at least one of Ag, Al, Yb, Ti, Mg, Ni, Li, Ca, Cu, LiF/Ca, LiF/Al, MgAg, and CaAg. The at least one selected material can be formed as a thin film having a thickness of few to several nm so that the thin film has a certain degree of transmittance. 
     The thin film encapsulating layer  130  can include at least one inorganic layer and at least one organic layer. The at least one inorganic layer can be formed of a metal oxide, a metal nitride, a metal carbide, or a combination thereof, and the at least one organic layer can be formed of any one selected from epoxy, acrylate, and urethane acrylate. 
     Referring to  FIGS. 2C and 2D , the method of manufacturing the OLED display  1  according to an exemplary embodiment include forming a light-blocking material  140 ′ having the first thickness t 1  in the non-emission area NA and the emission area EA on the thin film encapsulating layer  130 . The method also includes irradiating light onto the non-emission area NA by using a mask M including a hole H corresponding to the non-emission area NA, and forming the second light-blocking unit  142  having the second thickness t 2  by developing the light-blocking material  140 ′ and thus removing a portion of the light-blocking material  140 ′ formed in the emission area EA. 
     The first thickness t 1  can be about at least 0.8 μm, and light can be irradiated onto only the non-emission area NA by using the mask M including the hole H corresponding to the non-emission area NA. 
     The light-blocking material  140 ′ can be a photosensitive resin including black pigments. The resin can be a material that is cured and not easily dissolved when light is irradiated thereon. Therefore, the light-blocking material  140 ′ that is formed in the non-emission area NA, onto which light is irradiated, can be cured and not dissolved when a developing process is performed. 
     However, the light-blocking material  140 ′ that is formed in the emission area EA, onto which light is not irradiated, can be removed by the developing process. By adjusting a developing time, the second light-blocking unit  142  can be formed to have the second thickness t 2  of about 0.1 μm to about 0.5 μm in the emission area EA. For example, a developing time necessary for removing a predetermined thickness of the light-blocking material  140 ′ is calculated based on an already known developing time necessary for removing 1 μm of the light-blocking material  140 ′, and the second light-blocking unit can be formed by performing the developing process performed only for the calculated developing time. 
     According to the process above, the second light-blocking unit  142  can be formed to have the second thickness t 2 , and an area that is not developed due to light irradiation can correspond to the first light-blocking unit  141  having the first thickness t 1 . 
     After forming the black matrix  140  that includes the first and second light-blocking units  141  and  142 , the overcoat film  150  (of  FIG. 1 ) and the window  160  (of  FIG. 1 ) can be formed on the black matrix  140 . 
       FIG. 3  is a cross-sectional view schematically illustrating an OLED display  2  according to an exemplary embodiment.  FIGS. 4A and 4B  are cross-sectional views sequentially illustrating a part of a method of manufacturing the OLED display  2  of  FIG. 3 . 
     Referring to  FIG. 3 , the OLED display  2  includes a substrate  210  defined as an emission area EA and a non-emission area NA and pixel electrodes  221   a ,  221   b , and  221   c  formed on the emission area EA of the substrate  210 . The OLED display  2  also includes intermediate layers  223   a ,  223   b , and  223   c  including organic emission layers and formed on the pixel electrodes  221   a ,  221   b , and  221   c , and an opposite electrode  225  formed on the emission area EA and the non-emission area NA to cover the intermediate layers  223   a ,  223   b , and  223   c . The OLED display  2  further includes a black matrix  240  including a first light-blocking unit or first light-blocking portion  241  formed on an area corresponding to the non-emission area NA and a second light-blocking unit or second light-blocking portion  242  formed in an area corresponding to at least the emission area EA and having a greater light transmittance than the first light-blocking unit  241 , on the opposite electrode  225 . 
     A thin film encapsulating layer  230  can be formed between the opposite electrode  225  and the black matrix  240 , and a PDL  222  can cover both edges of each of the pixel electrodes  221   a ,  221   b , and  221   c.    
     The black matrix  240  can be formed on the thin film encapsulating layer  230 , and can include the first light-blocking unit  241  located in the non-emission area NA and the second light-blocking unit  242  located in the emission area EA and the non-emission area NA. 
     The second light-blocking unit  242  can be formed in the emission area EA and the non-emission area NA on the thin film encapsulating layer  230 , and the first light-blocking unit  241  can be formed in the non-emission area NA on the second light-blocking unit  242 . 
     According to an exemplary embodiment, the first light-blocking unit  241  and the second light-blocking unit  242  can be formed of a substantially identical material, for example, a photosensitive resin including black pigments. The first light-blocking unit  241  can have a fourth thickness t 4  and the second light-blocking unit  242  can have a fifth thickness t 5  that are about 0.1 μm to about 0.5 μm. The sum of the fourth thickness t 4  and the fifth thickness t 5  can be about 0.8 μm or more. However, depending on embodiments, the fifth thickness t 5  can have a thickness of less than about 0.1 μm or greater than about 0.5 μm, and the sum of the fourth and fifth thicknesses t 4  and t 5  can be less than about 0.8 μm. 
     That is, on the thin film encapsulating layer  230 , the second light-blocking unit  242  and the first light-blocking unit  241  can be sequentially formed in the non-emission area NA, but only the second light-blocking unit  242  can be formed in the emission area EA. 
     The black matrix  240  can prevent external light reflection so that visibility of the OLED display  2  is improved. According to an exemplary embodiment, respective visible light transmittances of the first light-blocking unit  241  and the second light-blocking unit  242  that are sequentially formed can be about 0.2% or less, and a visible light transmittance of the second light-blocking unit  242  can be about 40% to about 70%. 
     Referring to  FIGS. 4A and 4B , the method of manufacturing the OLED display  2  includes forming the black matrix  240  on the thin film encapsulating layer  230 . The forming of the black matrix  240  can include forming the second light-blocking unit  242  to have the fifth thickness t 5  in the emission area EA and the non-emission area NA, and forming the first light-blocking unit  241  to have the fourth thickness t 4  on the non-emission area NA of the second light-blocking unit  242 . The fifth thickness t 5  can be about 0.1 μm to about 0.5 μm, and the sum of the fourth thickness t 4  and the fifth thickness t 5  can be about 0.8 μm or more. However, depending on embodiments, the fifth thickness t 5  can have a thickness of less than about 0.1 μm or greater than about 0.5 μm, and the sum of the fourth and fifth thicknesses t 4  and t 5  can be less than about 0.8 μm. 
     An overcoat film  250  can be formed on the black matrix  240 , and a window  260  can be formed on the overcoat film  250 . 
     Since elements included in the OLED display  2  of  FIG. 2  except for the black matrix  240  are the same as those included in the OLED display  1  of  FIG. 1 , detailed descriptions of the elements will not be repeated. 
       FIG. 5  is a cross-sectional view schematically illustrating an OLED display  3  according to an exemplary embodiment.  FIGS. 6A and 6B  are cross-sectional views sequentially illustrating a part of a method of manufacturing the OLED display  3  of  FIG. 5 . 
     Referring to  FIG. 5 , the OLED display  3  includes a substrate  310  defined as an emission area EA and a non-emission area NA, pixel electrodes  321   a ,  321   b , and  321   c  formed on the emission area EA of the substrate  310 , and intermediate layers  323   a ,  323   b , and  323   c  including organic emission layers and formed on the pixel electrodes  321   a ,  321   b , and  321   c . The OLED display  3  also includes an opposite electrode  325  formed on the emission area EA and the non-emission area NA to cover the intermediate layers  323   a ,  323   b , and  323   c , and a black matrix  340  including a first light-blocking unit or first light-blocking portion  341  formed on an area corresponding to the non-emission area NA and a second light-blocking unit or second light-blocking portion  342  formed in an area corresponding to at least the emission area EA and having a greater light transmittance than the first light-blocking unit  341 , on the opposite electrode  325 . 
     A thin film encapsulating layer  330  can be formed between the opposite electrode  325  and the black matrix  340 , and a PDL  322  can cover both edges of each of the pixel electrodes  321   a ,  321   b , and  321   c.    
     The black matrix  340  can be formed on the thin film encapsulating layer  330 , and can include the first light-blocking unit  341  located in the non-emission area NA and the second light-blocking unit  342  located in the emission area EA. 
     The first and second light-blocking units  341  and  342  can have substantially the same thickness, i.e., a third thickness t 3 , which is about 0.8 μm or more. Each of the first and second light-blocking units  341  and  342  can be formed as a resin  340   a  including black pigments  340   b . A density of the black pigments  340   b  included in the first light-blocking unit  341  can be greater than a density of the black pigments  340   b  included in the second light-blocking unit  342 . A visible light transmittance (or light transmittance) of the first light-blocking unit  341  can be about 0.2% or less and a visible light transmittance (or light transmittance) of the second light-blocking unit  342  can be about 40% to about 70%. However, depending on embodiments, the visible light transmittance of the first light-blocking unit  341  can be greater than about 0.2% and the visible light transmittance of the second light-blocking unit  342  can be less than about 40% or greater than about 70%. 
     That is, by making the densities of the black pigments  340   b  included in the resin  340   a  to be different, respective transmittances of the first light-blocking unit  341  and the second light-blocking unit  342  can be different. 
     Referring to  FIGS. 6A and 6B , the method of manufacturing the OLED display  3  according to an exemplary embodiment includes forming the black matrix  340  on the thin film encapsulating layer  330 . The forming of the black matrix  340  can include forming the first light-blocking unit  341  to have a third thickness t 3  in the non-emission area NA, and forming the second light-blocking unit  342  to have the third thickness t 3  that is substantially the same as that of the first light-blocking unit  341  in the emission area EA. 
     That is, first, the first light-blocking unit  341  is formed by using a material in which the black pigments  340   b  have a large density. Then, by using the first light-blocking unit  341  as banks, a material in which the black pigments  340   b  have a small density is filled in spaces defined by the first light-blocking unit  341  by using a method such as inkjet printing. Thus, the second light-blocking unit  342  can be formed. 
     An overcoat film  350  can be formed on the black matrix  240 , and a window  360  can be formed on the overcoat film  350 . 
     Since elements included in the OLED display  3  of  FIG. 5  except for the black matrix  340  are the same as those included in the OLED display  1  of  FIG. 1 , detailed descriptions of the elements will not be repeated. 
       FIG. 7  is a cross-sectional view schematically illustrating an OLED display  4  according to an exemplary embodiment.  FIG. 8  is a cross-sectional view illustrating a part of a method of manufacturing the OLED display  4  of  FIG. 7 . 
     Referring to  FIG. 7 , the OLED display  4  includes a substrate  410  defined as an emission area EA and a non-emission area NA, pixel electrodes  421   a ,  421   b , and  421   c  formed on the emission area EA of the substrate  410 , and intermediate layers  423   a ,  423   b , and  423   c  including organic emission layers and formed on the pixel electrodes  421   a ,  421   b , and  421   c . The OLED display  4  also includes an opposite electrode  425  formed on the emission area EA and the non-emission area NA to cover the intermediate layers  423   a ,  423   b , and  423   c , and a black matrix  440  including a first light-blocking unit or first light-blocking portion  441  formed on an area corresponding to the non-emission area NA and a second light-blocking unit or second light-blocking portion  442  formed in an area corresponding to the at least emission area EA and having a greater light transmittance than the first light-blocking unit  441 , on the opposite electrode  425 . A thin film encapsulating layer  430  can be formed between the opposite electrode  425  and the black matrix  440 , and a PDL  442  can cover both edges of each of the pixel electrodes  421   a ,  421   b , and  421   c.    
     The OLED display  4  can include an encapsulating substrate  470  that faces the substrate  410 . The black matrix  440  can be formed on a surface of the encapsulating substrate  470 , the surface which faces the substrate  410 . The black matrix  440  can include the first light-blocking unit  441  located in the non-emission area NA and the second light-blocking unit  442  located in the emission area EA. 
     The black matrix  440  can prevent external light reflection so that visibility of the OLED display  4  is improved. According to an exemplary embodiment, a visible light transmittance (or light transmittance) of the first light-blocking unit  441  can be about 0.2% or less, and a visible light transmittance (or light transmittance) of the second light-blocking unit  442  can be about 40% to about 70%. 
     According to an exemplary embodiment, the first and second light-blocking units  441  and  442  can be formed of a substantially identical material, for example, a photosensitive resin including black pigments. The first and second light-blocking units  441  and  442  can have different thicknesses so that there is a difference between respective visible light transmittances. That is, the first light-blocking unit  441  can have a first thickness t 1  and the second light-blocking unit  442  can have a second thickness t 2  that is less than the first thickness t 1 . 
     According to an exemplary embodiment, the first thickness t 1  is about 0.8 μm or more and the second thickness t 2  can be about 0.1 μm to about 0.5 μm. As described above, the first light-blocking unit  441  having the first thickness t 1  can have a visible light transmittance (or light transmittance) of about 0.2% or less, and the second light-blocking unit  442  having the second thickness t 2  can have a visible light transmittance (or light transmittance) of about 40% to about 70%. However, depending on embodiments, the visible light transmittance of the first light-blocking unit  341  can be greater than about 0.2% and the visible light transmittance of the second light-blocking unit  342  can be less than about 40% or greater than about 70%. 
     Referring to  FIG. 8 , the method of manufacturing the OLED display  4  according to an exemplary embodiment includes after forming the encapsulating substrate  470  that faces the substrate  410 , forming the black matrix  440  on a surface of the encapsulating substrate  470 , the surface which faces the substrate  410 , and aligning the substrate  410  and the encapsulating substrate  470 . 
     The black matrix  440  can be formed by using the method described with reference to  FIGS. 2C and 2D . 
     Since elements included in the OLED display  4  of  FIG. 7  except for the encapsulating substrate  470  and the black matrix  440  are the same as those included in the OLED display  1  of  FIG. 1 , detailed descriptions of the elements will not be repeated. 
       FIG. 9  is a graph illustrating an external light reflectance and a transmittance of light emitted from an intermediate layer versus wavelengths, in the OLED display  1  of  FIG. 1 . 
     Referring to  FIG. 9 , an average of the external light reflectance of the OLED display  1  is about 3.56%, and an average of the transmittance of light emitted from the intermediate layers  123   a ,  123   b , and  123   c  is about 49.9%. 
     That is, the OLED display  1  can efficiently prevent external light reflection without using a polarizer. Also, the light extraction efficiency of the OLED display  1  can be similar to or greater than the light extraction efficiency when a polarizer having a light transmittance of about 40% to about 50% is used. 
     The OLED displays  1  to  4  according to exemplary embodiments can be manufactured as flexible displays by not using a polarizer but respectively including the black matrices  140 ,  240 ,  340 , and  440  formed in the emission area EA and the non-emission area NA. Thus, visibility of the OLED displays  1  to  4  can have improved visibility by efficiently reducing external light reflection. 
     It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. 
     While the inventive technology has been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details can be made therein without departing from the spirit and scope as defined by the following claims.