Abstract:
The present invention relates to a substrate for color conversion, a manufacturing method therefor, and a display device comprising the same and, more specifically, to a substrate for color conversion for not only securing the long-term stability of quantum dots but also exhibiting excellent color conversion efficiency, a manufacturing method therefor, and a display device comprising the same. To this end, the present invention provides a substrate for color conversion, a manufacturing method therefor, and a display device, the substrate for color conversion comprising: a thin plate glass; a coating layer for quantum dots formed on one surface of the thin plate glass; a light guide plate disposed to face the coating layer for quantum dots, a light emitting diode being disposed on the sides thereof; and a sealing material which is formed between the thin plate glass and the light guide plate and which blocks the coating layer for quantum dots from the outside.

Description:
BACKGROUND 
       [0001]    Field 
         [0002]    The present disclosure generally relates to a color conversion substrate, a method of fabricating the same, and a display device including the same. More particularly, the present disclosure relates to a color conversion substrate able to obtain long-term stability in quantum dots (QDs) and a superior degree of color conversion efficiency in the color conversion substrate, a method of fabricating the same, and a display device including the same. 
         [0003]    Description of Related Art 
         [0004]    A light-emitting diode (LED) is a semiconductor device formed of a compound such as gallium arsenide (GaAs) to emit light when an electrical current is applied thereto. The LED uses a p-n junction semiconductor structure into which minority carriers, such as electrons or holes, are injected, such that light is generated by the recombination of electrons and holes. 
         [0005]    The characteristics of LEDs include low power consumption, a relatively long lifespan, the ability to be mounted in cramped spaces, and strong resistance to vibrations. LEDs are commonly used in display devices and in the backlight units of display devices. Recently, research into applying LEDs to general illumination devices has been undertaken. In addition to monochromatic LEDs, such as red, blue, or green LEDs, white LEDs have also come onto the market. In particular, a sharp increase in demand for white LEDs is anticipated, in line with the application of white LEDs to vehicle lighting devices and general lighting devices. 
         [0006]    In the field of LED technology, white light is commonly generated using two main methods. The first method to generate white light includes disposing monochromatic LEDs, such as red, green, and blue LEDs, adjacently to each other such that various colors of light emitted by the monochromatic LEDs are mixed. However, color tones may change depending on the environment in which such devices are used, since individual monochromatic LEDs have different thermal or temporal characteristics. In particular, color stains may occur, making it difficult to uniformly mix different colors of light. The second method to generate white light includes applying a fluorescent material to an LED and mixing a portion of initial light emitted by the LED and secondary light of which wavelength has been converted by the fluorescent material. For example, a fluorescent material generating yellowish-green or yellow light may be used as a light excitation source on a blue LED, whereby white light can be produced by mixing blue light emitted by the blue LED and yellowish-green or yellow light excited by the fluorescent material. At present, the second method of realizing white light utilizing a blue LED and a fluorescent material is generally used. 
         [0007]    Recently, quantum dots (QDs) have been used for color conversion to produce white light. QDs generate relatively strong light within a narrow wavelength, the light being stronger than light generated from a typical fluorescent material. In general, a QD-LED backlight unit generates white light by irradiating blue light emitted by a blue LED onto yellow QDs, and applies the white light to a liquid crystal display (LCD) as backlight. LCDs using such a QD-LED backlight unit have high potential as new displays, since the characteristics of such LCDs include superior color reproduction unlike those using a traditional backlight using LEDs only, the ability to realize full color comparable to that of organic light emitting diodes (OLEDs), as well as lower fabrication costs and higher manufacturing productivity than OLED TVs. 
         [0008]    However, when QDs are continuously exposed to oxygen and moisture in an external air gap, defects may be formed on the surface of QDs, leading to problems, such as reduction in color conversion efficiency and change in color coordinates. Therefore, it is important to ensure the thermal stability of QDs and isolate QDs from the external air gap in order to apply QDs to a display device as a color (wavelength) conversion material. 
       RELATED ART DOCUMENT 
       [0009]    Patent Document 1: United States Patent Application Publication No. 20120113672 (May 10, 2012) 
       BRIEF SUMMARY 
       [0010]    Various aspects of the present disclosure provide a color conversion substrate able to obtain long-term stability and a superior degree of color conversion efficiency in quantum dots (QDs) and a superior degree of color conversion efficiency in the color conversion substrate, a method of fabricating the same, and a display device including the same. 
         [0011]    According to an aspect, a color conversion substrate includes: a thin glass plate; a QD coating layer disposed on one surface of the thin glass plate; a light guide plate disposed to face the QD coating layer, wherein a light-emitting diode (LED) is disposed on a side of the light guide plate; and a sealant disposed between the thin glass plate and the light guide plate to isolate the QD coating layer from an external environment. 
         [0012]    The QD coating layer may have an embossed pattern on a surface thereof facing the light guide plate. 
         [0013]    The thin glass plate may have an embossed pattern on the other surface thereof. 
         [0014]    The light guide plate may implemented as a glass light guide plate or a polymer light guide plate. 
         [0015]    The sealant may be formed of a frit when the light guide plate is the glass light guide plate or is formed of an epoxy when the light guide plate is the polymer light guide plate. 
         [0016]    The color conversion substrate may further include a moisture absorber disposed between the QD coating layer and the sealant. 
         [0017]    According to another aspect, a color conversion substrate includes: a first thin glass plate; a QD coating layer disposed on the bottom surface of the first thin glass plate; a second thin glass plate in close contact with the bottom surface of the QD coating layer; a sealant disposed between the first thin glass plate and the second thin glass plate to isolate the QD coating layer from an external environment; and a light guide plate disposed under the second thin glass plate. An LED is disposed on a side of the light guide plate. 
         [0018]    The QD coating layer may have an embossed pattern on the bottom surface thereof. 
         [0019]    The first thin glass plate may have an embossed pattern on the top surface thereof. 
         [0020]    The second thin glass plate may have an embossed pattern on the bottom surface thereof. 
         [0021]    The sealant may be formed of a frit. 
         [0022]    The color conversion substrate may further include a moisture absorber disposed between the QD coating layer and the sealant. 
         [0023]    According to further another aspect, a display device includes: the above-stated color conversion substrate; a display panel disposed over the color conversion substrate; and an LED disposed on a side of the light guide plate of the color conversion substrate, and serving, together with the color conversion substrate, as a side emitting backlight unit. 
         [0024]    The display panel may be implemented as a liquid crystal display (LCD) panel. 
         [0025]    According to yet another aspect, a method of fabricating a color conversion substrate includes: forming a QD coating layer by coating a thin glass plate with a paste containing QDs; disposing a second thin glass plate or a light guide plate in a position facing the thin glass plate such that the QD coating layer is sandwiched between the second thin glass plate or the light guide plate and the thin glass plate; and hermetically bonding a periphery of a surface of the thin glass plate to a periphery of a surface of the second thin glass facing the surface of the thin glass plate or to a periphery of a surface of the light guide plate facing the surface of the thin glass plate by means of a sealant. 
         [0026]    The operation of forming the QD coating layer may include forming an embossed pattern on the surface of the QD coating layer while adjusting the degree of curing the paste. 
         [0027]    The sealant may be applied on the thin glass plate in the operation of forming the QD coating layer or may be applied on the second thin glass plate or the light guide plate in the operation of disposing the second thin glass plate or the light guide plate. 
         [0028]    The sealant may be formed of a frit or an epoxy. 
         [0029]    The method may further include disposing a moisture absorber around the QD coating layer. 
         [0030]    As set forth above, a frit material and an epoxy material having superior sealing characteristics are applied as a sealant. It is therefore possible to protect the inner QD coating layer from both moisture and oxygen, thereby obtaining long-term stability of the QDs. 
         [0031]    In addition, according to the present disclosure, the pattern formed on the surface of the QD coating layer scatters light that has been emitted by the LEDs and guided by the light guide plate before the light is wavelength-converted by the QDs. This enables the light to be additionally wavelength-converted, thereby improving color conversion efficiency. Furthermore, a pattern is formed on one surface of the thin glass plate exposed to air, with the QD coating layer formed on the other surface of the thin glass plate. It is possible to reduce the amount of light totally reflected from the interface between the thin glass plate and the air while the light is passing through the thin glass plate after passing through the QD coating layer. This can consequently increase the color conversion efficiency using the QDs and, furthermore, can reduce the number of LEDs used as a light source and the amount of energy consumed, whereby a high-efficient environmentally-friendly display device can ultimately be realized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a cross-sectional view schematically illustrating a color conversion substrate and a display device including the same according to an exemplary embodiment; 
           [0033]      FIG. 2  illustrates simulated light diffusion patterns in a case in which an embossed pattern is formed on the surface of a QD coating layer (left) and a case in which the surface of the QD coating layer is flat (right); and 
           [0034]      FIG. 3  is a cross-sectional view schematically illustrating a color conversion substrate and a display device including the same according to another exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Reference will now be made in detail to a color conversion substrate, a method of fabricating the same, and a display device including the same according to the present disclosure, embodiments of which are illustrated in the accompanying drawings and described below, so that a person skilled in the art to which the present disclosure relates could easily put the present disclosure into practice. 
         [0036]    Throughout this document, reference should be made to the drawings, in which the same reference numerals and symbols will be used throughout the different drawings to designate the same or like components. In the following description, detailed descriptions of known functions and components incorporated herein will be omitted in the case that the subject matter of the present disclosure is rendered unclear by the inclusion thereof. 
         [0037]    As illustrated in  FIG. 1 , a color conversion substrate  100  according to an embodiment is configured to convert the color (wavelength) of a portion of light emitted by one or more light-emitting diodes (LEDs) used as a backlight source of a display device, for example, a liquid crystal display (LCD). According to the present embodiment, the color conversion substrate  100  is disposed to the rear of a display panel  20  such as an LCD panel, and forms, together with one or more LEDs (hereinafter referred to as “LEDs”)  10 , an LCD backlight unit (BLU) radiating light toward the display panel  20 . Although not illustrated in the drawings, each of the LEDs  10  may include an LED body and an LED chip. The LED body is a structure having a hollow portion in a specific shape, providing a structural space for accommodation of the LED chip. The LED body has wires and a lead frame by which the LED chip is electrically connected to an external power source. The LED chip is a light source emitting light when an electrical current is applied thereto by the external power source, is mounted on the LED body, and is connected to the external power source via the wires and the lead frame. The LED chip is implemented as a forward junction of an n-semiconductor layer that provides electrons and a p-semiconductor layer that provides holes. In the present embodiment, the backlight unit is implemented as a side emitting backlight. Accordingly, the LEDs  10  are disposed on one side of the color conversion substrate  100  to emit light toward the color conversion substrate  100 . 
         [0038]    In this manner, the color conversion substrate  100  according to the present embodiment forming the backlight unit of the display panel  20  together with the LEDs  10  includes a thin glass plate  110 , a quantum dot (QD) coating layer  120 , a light guide plate  130 , and a sealant  140 . 
         [0039]    The thin glass plate  110  protects the QD coating layer  120  disposed on the bottom surface thereof (when referring to  FIG. 1 ). In addition, the thin glass plate  110  serves as a path along which light emitted by the LEDs  10  passes or exits in the direction of the display panel  20  disposed above the thin glass plate  110 . In addition, the thin glass plate  110  is bonded to the light guide plate  130  by the sealant  140 , thereby isolating the QD coating layer  120  from the external environment. The thin glass plate  110  may formed of a material selected from among, but is not limited to, silicate glass, silica glass, borosilicate glass, and non-alkali glass, with a thickness of  0 . 3  mm or less. According to the present embodiment, the thin glass plate  110  provided as above can reduce the thickness of the color conversion substrate  100 , thereby reducing the thickness of the display device. 
         [0040]    According to the present embodiment, a pattern  111  having an embossed structure is formed on the top surface of the thin glass plate  110 , i.e. the surface of the thin glass plate  110  facing the display panel  20 . Although the pattern  111  is illustrated as having a semicircular cross-section in the present embodiment, this is merely illustrative, and the pattern  111  may have a variety of cross-sectional shapes. 
         [0041]    The pattern  111  formed on the top surface of the thin glass plate  110  as above can reduce the amount of light that is totally reflected from the interface between the thin glass plate  110  and air while the light is passing through the thin glass plate  110 . This can consequently increase the color conversion efficiency of QDs in the QD coating layer  120  and, furthermore, can reduce the number of LEDs  10  used as the light source and the amount of energy consumed, whereby a highly-efficient environmentally-friendly display device can ultimately be realized. 
         [0042]    The QD coating layer  120  is disposed on the bottom surface of the thin glass plate  110 . In addition, the QD coating layer  120  is hermetically sealed by the thin glass plate  110 , the light guide plate  130  and the sealant  140 , thereby being prevented from being exposed to the air. According to the present embodiment, it is possible to protect the QD coating layer  120  from both moisture and oxygen, thereby obtaining long-term stability in the QD coating layer  120 . The QDs of the QD coating layer  120  convert the wavelength of light emitted by the LEDs  10 , thereby generating wavelength-converted light, i.e. fluorescent light. According to the present embodiment, since the LEDs  10  are implemented as blue LEDs, the QD coating layer  120  may be formed of a QD material converting the wavelength of a portion of light emitted by the blue LEDs  10  into yellow light. 
         [0043]    According to the present embodiment, a pattern  121  having an embossed structure is formed on the bottom surface of the QD coating layer  120 , i.e. on the surface of the QD coating layer  120  facing the light guide plate  130 . Although the embossed pattern  121  has a triangular cross-section as illustrated in  FIG. 1 , the embossed pattern  121  may have a variety of other shapes. Thus, the shape of the pattern  121  formed on the QD coating layer  120  is not limited to any specific shape. The embossed pattern  121  is formed on the bottom surface of the QD coating layer  120  through which light guided by the light guide plate  130  enters the QD coating layer  120 , and thus serves to scatter the light to be wavelength-converted by the QD coating layer  120 . This consequently enables additional wavelength conversion, thereby improving color conversion efficiency. 
         [0044]      FIG. 2  illustrates simulated light diffusion patterns demonstrating the effects of the pattern  121  formed on the surface of the QD coating layer  120 . It is apparent that light is diffused in the case in which the pattern  121  is formed on the surface of the QD coating layer  120  (left), whereas substantially no light is diffused in the case in which the surface of the QD coating layer is flat (right). 
         [0045]    The light guide plate (LGP)  130  is disposed to face the QD coating layer  120 . The light guide plate  130  and the thin glass plate  110  are bonded by means of the sealant  140 , thereby sealing the QD coating layer  120 . In addition, the light guide plate  130  distributes light that is incident thereto after being emitted by a point light source of the LEDs  10 , uniformly over the entire area of the display panel  20 . That is, the light guide plate  130  guides the light emitted by the LEDs  10  in the direction of the QD coating layer  120  and the display panel  20 . 
         [0046]    According to the present embodiment, the light guide plate  130  may be implemented as a glass light guide plate or a polymer light guide plate. In addition, the thickness of the light guide plate  130  may be 1.0 mm or less. 
         [0047]    The sealant  140  is disposed between the thin glass plate  110  and the light guide plate  130 . Specifically, the sealant  140  is disposed between the bottom periphery of the thin glass plate  110 , laterally spaced apart from the QD coating layer  120  on the bottom surface of the thin glass plate  110  and the top periphery of the light guide plate  130  corresponding to the bottom periphery. The sealant  140  disposed between the thin glass plate  110  and the light guide plate  130  is in a shape encircling the side surfaces of the QD coating layer  120 , serving, together with the thin glass plate  110  and the light guide plate  130 , to isolate the QD coating layer  120  from the external environment. When the light guide plate  130  is implemented as a glass light guide plate, the sealant  140  may be formed of a frit having superior ability in being bonded to the thin glass plate  110  and the glass light guide plate. When the light guide plate  130  is implemented as a polymer light guide plate, the sealant  140  may be formed of an epoxy. 
         [0048]    The color conversion substrate  100  according to the present embodiment may include a moisture absorber  150  within an enclosed space defined by the thin glass plate  110 , the sealant  140 , and the light guide plate  130 . When the moisture absorber  150  is disposed adjacently to the QD coating layer  120  within the enclosed space defined by the thin glass plate  110 , the sealant  140 , and the light guide plate  130 , the moisture absorber  150  can prevent the QD coating layer  120  from being exposed to moisture, thereby further improving long-term stability of the QD coating layer  120 . 
         [0049]    Hereinafter, a color conversion substrate according to another exemplary embodiment will be described with reference to  FIG. 3 . 
         [0050]      FIG. 3  is a cross-sectional view schematically illustrating the color conversion substrate according to the another embodiment and a display device including the same. 
         [0051]    As illustrated in  FIG. 3 , a color conversion substrate  200  includes a first thin glass plate  210 , a QD coating layer  120 , a second thin glass plate  230 , a sealant  140 , and a light guide plate  240 . 
         [0052]    The first thin glass plate  210  may formed of one material selected from among, but is not limited to, silicate glass, silica glass, borosilicate glass, and non-alkali glass, with a thickness of 0.5 mm or less, like the thin glass plate ( 110  in  FIG. 1 ) according to the former embodiment. In addition, a pattern  211  having an embossed structure is formed on the top surface of the first thin glass plate  210 . Descriptions of the functions and effects of the pattern  211  identical to those of the pattern ( 111  in  FIG. 1 ) of the thin glass plate  110  according to the former embodiment will be omitted. 
         [0053]    The QD coating layer  120  is disposed on the bottom layer of the first thin glass plate  210 . Descriptions of the QD coating layer  120  identical to the QD coating layer ( 120  in  FIG. 1 ) according to the former embodiment will be omitted. 
         [0054]    The second thin glass plate  230  is in close contact with the bottom surface of the QD coating layer  120 . The thickness and type of the second thin glass plate  230  may be identical to those of the first thin glass plate  210 . A pattern  231  having an embossed structure  231  is disposed on the bottom surface of the second thin glass plate  230 . The pattern  231  faces the light guide plate  240 . The pattern  231  disposed on the bottom surface of the second thin glass plate  230  facing the light guide plate  240  increases lengths of paths along which light guided by the light guide plate  240  travels. This can consequently increase the contact between the light and the QD coating layer  120 , thereby further increasing color conversion efficiency. 
         [0055]    Unlike the former embodiment, the sealant  140  according to the present embodiment is disposed between the first thin glass plate  210  and the second thin glass plate  230  in order to isolate the QD coating layer  120  from the external environment. The sealant  140  may be formed of a frit having superior ability to be bonded to the first thin glass plate  210  and the second thin glass plate  230 . 
         [0056]    According to the present embodiment, the second thin glass plate  230  is bonded to the first thin glass plate  210  by means of the sealant  140 , thereby sealing the QD coating layer  120  disposed on the bottom surface of the first thin glass plate  210 . Due to this configuration, the light guide plate  240  is disposed under the second thin glass plate  230  in order to guide light emitted by LEDs  10  in the direction of the QD coating layer  120 . 
         [0057]    As in the former embodiment, the color conversion substrate  200  according to the present embodiment includes a moisture absorber  150  disposed between the QD coating layer  120  and the sealant  140 . 
         [0058]    Hereinafter, a method of fabricating a color conversion substrate according to an exemplary embodiment will be described. The reference numerals in  FIG. 1  and  FIG. 3  will be referred to for the components of the color conversion substrate. 
         [0059]    First, a QD coating layer  120  is formed by coating a thin glass plate  110  with a paste containing QDs. In this case, a pattern  121  in an embossed structure may be formed on the surface of the QD coating layer  120  by adjusting the degree of curing the paste. In addition, a pattern  111  in an embossed structure may be formed on the surface of the thin glass plate  110  facing away from the surface coated with the paste. 
         [0060]    Afterwards, the light guide plate  130  or a second thin glass plate  230  having a pattern  231  is disposed in a position facing the thin glass plate  110  such that the QD coating layer  120  is sandwiched between the light guide plate  130  or the second thin glass plate  230  and the thin glass plate  110 . At this time, after the QD coating layer  120  is formed on the thin glass plate  110 , a sealant  140  may be applied on the periphery of the thin glass plate  110  laterally spaced apart from the QD coating layer  120  or may be applied on the periphery of the second thin glass plate  230  or the light guide plate  130  that faces the thin glass plate  110 . 
         [0061]    Before the thin glass plate  230  or the light guide plate  130  is disposed in the position facing the QD coating layer  120 , a moisture absorber  150  may be applied to on thin glass plate  110  between the QD coating layer  120  and the applied sealant  140 , around the QD coating layer  120 . 
         [0062]    Finally, the thin glass plate  110  and the second thin glass plate  230  or the thin glass plate  110  and the light guide plate  130  are bonded to each other by firing the sealant  140  disposed therebetween, whereby the method of fabricating a color conversion substrate according to the present embodiment is completed. 
         [0063]    It is preferable that the sealant  140  be formed of a frit when bonding the thin glass plate  110  and the second thin glass plate  230  or the thin glass plate  110  and the light guide plate  130  formed of glass. It is preferable that the sealant  140  be formed of an epoxy when bonding the thin glass plate  110  and the light guide plate  130  formed of a polymer. 
         [0064]    In addition, when the QD coating layer  120  is sealed by bonding the thin glass plates  110  and  230 , the light guide plate  240  is disposed under the thin glass plate  230 , whereby light emitted by the LEDs  10  disposed on the side of the light guide plate  240  is guided to the QD coating layer  120 . 
         [0065]    The foregoing descriptions of specific exemplary embodiments of the present disclosure have been presented with respect to the drawings. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible for a person having ordinary skill in the art in light of the above teachings. 
         [0066]    It is intended therefore that the scope of the present disclosure not be limited to the foregoing embodiments, but be defined by the Claims appended hereto and their equivalents. 
       DESCRIPTION OF REFERENCE NUMERALS 
       [0067]      100 ,  200  : color conversion substrate 
         [0068]      110  : thin glass plate 
         [0069]      120 : quantum dot (QD) coating layer 
         [0070]      130 ,  240  : light guide plate 
         [0071]      140  : sealant 
         [0072]      150  : moisture absorber 
         [0073]      210  : first thin glass plate 
         [0074]      230  : second thin glass plate 
         [0075]      111 ,  121 ,  211 ,  231  : pattern 
         [0076]      10  : LED 
         [0077]      20  : display panel