Patent Publication Number: US-10330265-B2

Title: Front light source and display device comprising the front light source

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Patent Application No. 201710251061.9 filed on Apr. 17, 2017 in the State Intellectual Property Office of China, the disclosure of which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of display technology, and particularly, to a front light source and a display device comprising the front light source. 
     BACKGROUND 
     A reflective display device can display a picture by utilizing environment light as an illumination source. In practical application of the reflective display device, when being in a weak light environment or in a darkroom environment, the reflective display device has lower brightness and poor display effect. 
     In order to obtain good display effect in the weak light environment or in the darkroom environment, generally, a front light source is added into the reflective display device to assist displaying of the reflective display device. However, the front light source in a conventional reflective display device is usually achieved by cooperating a scattering film of the reflective display device with a front light guide plate. In the front light source of such structure, outgoing of light occurs in both sides of the light guide plate, which leads to dramatically decrease of the contrast in a dark state displaying (namely in the weak light environment or in the darkroom environment), thereby causing reduced colour gamut and poor display effect. 
     SUMMARY 
     According to one aspect of embodiments of the present disclosure, there is provided a front light source comprising: 
     a transparent substrate; 
     a plurality of light source elements provided on the transparent substrate; and 
     a plurality of light absorbing elements provided at front sides of the plurality of light source elements; 
     wherein, the plurality of light absorbing elements and the plurality of light source elements are in a one-to-one correspondence, an orthographic projection of each of the light source elements onto the transparent substrate is within an orthographic projection of one of the light absorbing elements corresponding to the each light source element onto the transparent substrate, and an area of the orthographic projection of the each of the light source elements onto the transparent substrate is smaller than an area of the orthographic projection of the one of the light absorbing elements corresponding to the each light source element onto the transparent substrate. 
     In some embodiments, the front light source further comprises: a plurality of quantum dot elements provided in the transparent substrate, 
     wherein, the plurality of quantum dot elements and the plurality of light source elements are in a one-to-one correspondence, and an orthographic projection of each of the light source elements onto the transparent substrate is within an orthographic projection of one of the quantum dot elements corresponding to the each light source element onto the transparent substrate. 
     In some embodiments, each of the light source elements comprises a light source element for emitting blue light, and each of the quantum dot elements comprises quantum dots for emitting red light by being excited with the blue light and quantum dots for emitting green light by being excited with the blue light, the quantum dots for emitting red light and the quantum dots for emitting green light being mixed at a predetermined proportion. 
     In some embodiments, the plurality of light source elements are provided in array on the transparent substrate, and pitches between every two adjacent light source elements are configured so that a light emitted by the front light source is uniformly distributed. 
     In some embodiments, the pitches between every two adjacent light source elements are the same and are in the range of 1 millimeter˜2.5 millimeters. 
     In some embodiments, the front light source further comprises: a reflecting element provided between each of the light source elements and a corresponding one of the light absorbing elements, and configured to reflect light emitted by the light source element towards a direction away from the corresponding one light absorbing element. 
     In some embodiments, each of the light absorbing elements has a size of not more than 70 μm in a direction parallel to the transparent substrate. 
     In some embodiments, a size of each of the quantum dot elements in a direction parallel to the transparent substrate is greater than a size of one of the light source elements corresponding to the each quantum dot element in the direction parallel to the transparent substrate, and a difference between the size of each of the quantum dot elements in the direction parallel to the transparent substrate and the size of one of the light source elements corresponding to the each quantum dot element in the direction parallel to the transparent substrate is determined based on a distance between the quantum dot element and the one of the light source elements corresponding to the quantum dot element in a direction perpendicular to the transparent substrate. 
     In some embodiments, an orthographic projection of each of the quantum dot elements onto the transparent substrate is within an orthographic projection of one of the light absorbing elements corresponding to the each quantum dot element onto the transparent substrate, and an area of the orthographic projection of each of the quantum dot elements onto the transparent substrate is smaller than an area of the orthographic projection of one of the light absorbing elements corresponding to the each quantum dot element onto the transparent substrate. 
     In some embodiments, the front light source further comprises: connection lines electrically connected to the plurality of light source elements, wherein, the connection lines are provided on the transparent substrate. 
     In some embodiments, a material for the connection line comprises an ITO or an IZO, and the connection line has a line width greater than or equal to 30 microns; or 
     the material for the connection line comprises a metal, and the connection line has a line width less than or equal to 3 microns and is treated with surface oxidation. 
     In some embodiments, the transparent substrate comprises a first layer of transparent film and a second layer of transparent film, the quantum dot elements are formed on the first layer of transparent film, and the second layer of transparent film is formed on the quantum dot elements in order to protect the quantum dot elements. 
     In some embodiments, an area of the orthographic projection of each of the light source elements onto the transparent substrate is smaller than an area of the orthographic projection of one of the quantum dot elements corresponding to the each light source element onto the transparent substrate. 
     According to one aspect of embodiments of the present disclosure, there is provided a display device, comprising: 
     the front light source of any one of the above embodiments; and 
     a display panel provided at a rear side of the front light source, wherein a reflecting component is provided at a side of the display panel away from the front light source. 
     In some embodiments, the plurality of light source elements are provided in array on the transparent substrate, and ratios of a distance between each of the light source elements and the reflecting component of the display panel in a direction perpendicular to the display panel to pitches between every two adjacent light source elements are in the range of 1:1˜1:1.5. 
     In some embodiments, the front light source further comprises: connection lines electrically connected to the plurality of light source elements, wherein, the connection lines are provided on the transparent substrate; wherein, 
     a size of the display device is less than or equal to 8 inches, and a material for the connection line comprises an ITO or an IZO; or 
     the size of the display device is greater than 8 inches, and the material for the connection line comprises a metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a structure of a display device according to an embodiment of the present disclosure; 
         FIG. 2  is a sectional view of a front light source according to an embodiment of the present disclosure; 
         FIG. 3  is a top view of the front light source in  FIG. 2 ; 
         FIG. 4  is a sectional view of a display device according to an embodiment of the present disclosure; and 
         FIG. 5  is a simulation diagram of optical distribution of a display device according to an exemplary embodiment of the present disclosure; 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Technical solutions of the present disclosure will be described hereinafter in detail in conjunction with the embodiments and with reference to the attached drawings, wherein the same or like reference numerals refer to the same or like elements. These embodiments disclosed in the drawings intend to explain general inventive concept of the present disclosure, but not to limit the present disclosure. 
     Further, in the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     It should be noted that in the description, expressions “on/above . . . ”, “formed on/above . . . ” and “provided on/above . . . ” may indicate one layer is formed or provided directly above another layer, or may indicate one layer is formed or provided indirectly above another layer, namely, there is/are other layer(s) provided between the two layers. 
     “Front” mentioned in the expression “front light source” used in the description indicates the light source is closer to a user than a display element of a display device in a normal use of the display device, that is, the light source is positioned in a side of the display element of the display element closing to the user. Accordingly, in the description, directional terminologies “front”, “rear”, “front side”, “rear side” and the likes indicate relatively positional relationships among these components or these elements, for example, “a first element is positioned in a front side of a second element” indicates that the first element is closer to a user than the second element in a normal use of a display device. 
       FIG. 1  is a schematic view showing a structure of a display device according to an embodiment of the present disclosure. Referring to  FIG. 1 , the display device may comprise a display panel  100 , a front light source  200  and an optical adhesive layer  300 . The optical adhesive layer  300  is configured to bond the display panel  100  and the front light source  200  together. The adhesive layer  300  may be formed of transparent optical adhesive material. 
       FIG. 2  is a sectional view of a front light source according to an embodiment of the present disclosure.  FIG. 3  is a top view of the front light source in  FIG. 2 . Referring to  FIG. 2  and  FIG. 3 , the front light source  200  may comprise: a transparent substrate  202 , a plurality of light source elements  204  provided on the transparent substrate  202 , and a plurality of light absorbing elements  206 . As shown in  FIG. 2 , the plurality of light absorbing elements  206  and the plurality of light source elements  204  are in a one-to-one correspondence, and the plurality of light absorbing elements  206  are provided at front sides of the plurality of light source elements  204 , that is, are provided at sides of the plurality of light source elements  204  closing to a user. An orthographic projection of each light source element  204  onto the transparent substrate  202  is within an orthographic projection of one light absorbing element  206  corresponding to the each light source element  204  onto the transparent substrate  202 , and an area of the orthographic projection of each light source element  204  onto the transparent substrate  202  is smaller than an area of the orthographic projection of the one light absorbing element  206  corresponding to the each light source element  204  onto the transparent substrate  202 . As a result, when the light source element  204  emits light, the light emitted by the light source element  204  cannot go out of a front side (namely an upper side in  FIG. 2 ) of the front light source because the size of the light absorbing element  206  is provided to be greater than the size of the light source element  204 . Hence, the light emitted by the light source element  204  only goes out of a rear side (namely a lower side in  FIG. 2 ) of the front light source, then is reflected by a reflecting component (see  FIG. 4 ) of the display panel, and finally goes out of the front side of the display device. With the above structure, the front light source according to the embodiments of the present disclosure achieves one-sided outgoing of light and increases the contrast of the front light source, thereby achieving a better display effect. 
     Optionally, the front light source  200  may further comprise a transparent cover plate  208  provided above the plurality of light absorbing elements  206  and configured to protect the light absorbing elements  206  and the light source elements  204 . 
     In one example, the light absorbing elements  206  may be black light absorbing elements, for instance, the light absorbing elements  206  may be formed of the same material as black matrix of a color film substrate. In one example, each of the light absorbing elements  206  has a size (such as size L BA  in  FIG. 2 ) of not more than 70 microns (μm) in a direction parallel to the transparent substrate  202 , so that the light absorbing elements  206  are invisible when the front light source  200  is observed by human eyes. 
     In one example, the transparent substrate  202  may be formed of transparent polyimide (PI) material, for instance, the transparent substrate  202  may include a transparent PI film. The transparent substrate  202  may have a thickness of 30 microns˜50 microns. 
     According to one exemplary embodiment of the present disclosure, the front light source  200  may adopt a luminescent solution of “monochromatic source+quantum dots (QDs)”. Quantum dots (QDs) generally refer to semiconductor nanocrystals having a diameter in the range of 1 nm˜10 nm. Quantum dots generally are semiconductor nano particles composed of group II-VI or III-V elements. Due to quantum confinement effect, quantum dots typically exhibit unique physical and chemical properties different from corresponding bulk phase materials and other molecular materials. Quantum dots can emit fluorescence by being excited by light having certain energy. Wavelength can be adjusted by changing size of the quantum dots. In addition, the quantum dots have excellent optical properties including broad and continuous absorption spectrum, narrow and symmetrical emission spectrum, excellent optical stability, high luminous efficiency. 
     Referring to  FIG. 2 , the front light source  200  may further comprise a plurality of quantum dot elements  210  provided in the transparent substrate  202 . The plurality of quantum dot elements  210  and the plurality of light source elements  204  are in a one-to-one correspondence, and an orthographic projection of each light source element  204  onto the transparent substrate  202  is within an orthographic projection of one of the quantum dot elements  210  corresponding to the each light source element  204  onto the transparent substrate  202 . Optionally, an area of the orthographic projection of each light source element  204  onto the transparent substrate  202  is smaller than an area of the orthographic projection of one of the quantum dot elements  210  corresponding to the each light source element  204  onto the transparent substrate  202 . 
     In one example, a size of each quantum dot element  210  in a direction parallel to the transparent substrate  202  is greater than a size of one of the light source elements  204  corresponding to the each quantum dot element in the direction parallel to the transparent substrate  202 , and a difference between the size of the each quantum dot element  210  in the direction parallel to the transparent substrate  202  and the size of the one of the light source elements  204  corresponding to the each quantum dot element in the direction parallel to the transparent substrate  202  is determined based on a distance between the each quantum dot element  210  and the one of the light source elements  204  corresponding to the each quantum dot element in a direction perpendicular to the transparent substrate  202 . Referring to  FIG. 2 , the direction parallel to the transparent substrate  202  may be X direction, the direction perpendicular to the transparent substrate  202  may be Z direction, the size L QD  of one quantum dot element  210  in the X direction is greater than the size L S  of one of the light source elements  204  corresponding to the one quantum dot element  210  in the X direction, and a difference between the L QD  and the L S  is determined based on a distance D 1  between the quantum dot element  210  and the light source element  204  in the Z direction. “A difference between the L QD  and the L S  is determined based on a distance D 1  between the quantum dot element  210  and the light source element  204  in the Z direction” refers to that, when the distance D 1  is relatively small, namely when the quantum dot element  210  is closer to the light source element  204 , the difference between the L QD  and the L S  may be set to be relatively small; and when the distance D 1  is relatively large, namely when the quantum dot element  210  is far away from the light source element  204 , the difference between the L QD  and the L S  may be set to be relatively large. With this configuration, it is ensured that light emitted by each light source element can be irradiated completely onto the quantum dot element  210  corresponding to the each light source element  204 , thereby increasing coefficient of utilization of the light emitted by the light source element. 
     In one example, the size L QD  of one quantum dot element  210  in the X direction is greater than the size L S  of one of the light source elements  204  corresponding to the one quantum dot element  210  in the X direction, by 2 microns˜5 microns. 
     In one example, an orthographic projection of each quantum dot element  210  onto the transparent substrate  202  is within an orthographic projection of one of the light absorbing elements  206  corresponding to the each quantum dot element  210  onto the transparent substrate  202 , and an area of the orthographic projection of the each quantum dot element  210  onto the transparent substrate  202  is smaller than an area of the orthographic projection of the one of the light absorbing elements  206  corresponding to the each quantum dot element  210  onto the transparent substrate  202 . In this way, the light absorbing element  206  can completely cover the quantum dot element  210 , thereby avoiding irradiation of environment light onto the quantum dot element to interfere with normal emission of the quantum dot. 
     In one example, the size L BA  of each light absorbing element  206  in the X direction is greater than the size L QD  of one of the quantum dot elements  210  corresponding to the each light absorbing element  206  in the X direction, by 2 microns˜5 microns. 
     In one example, the transparent substrate  202  may comprise a first layer  2021  of transparent film and a second layer  2022  of transparent film, and both the first layer  2021  of transparent film and the second layer  2022  of transparent film may be transparent PI films. The quantum dot elements  210  are formed on the first layer  2021  of transparent film, and the second layer  2022  of transparent film is formed on the quantum dot elements  210 . That is to say, all the quantum dot elements  210  are formed between the first layer  2021  of transparent film and the second layer  2022  of transparent film. With this design of double-layer configuration, the quantum dot elements can be protected from influence of external environment. In one example, the quantum dot elements  210  may be packaged within the transparent substrate  202  by screen printing or printing. 
     Specifically, each of the light source elements  204  may comprise a light source element emitting blue light, such as a light emitting diode (LED) emitting blue light, and each of the quantum dot elements  210  comprises quantum dots  2101  emitting green light by being excited with the blue light and quantum dots  2102  emitting red light by being excited with the blue light, mixed at a predetermined proportion. 
     In the abovementioned exemplary embodiment, the blue light emitted by the LED emitting blue light excites the quantum dots  2101  and the quantum dots  2102  respectively to emit green light and red light. In this way, once the quantum dots  2101  and the quantum dots  2102  are mixed at a predetermined proportion, the green light and the red light emitted by them after excitation are mixed at certain proportion, to obtain a mixed light after excitation as white light. It is found in experiments that, the above predetermined proportion may be one selected from a range from 1:2 to 2:1. That is to say, once the quantum dots  2101  emitting green light by being excited with the blue light and the quantum dots  2102  emitting red light by being excited with the blue light are mixed at a proportion selected from the range from 1:2 to 2:1, light-emitting elements composed of the blue light LED and the green light QDs and the red light QDs can generate standard white light. Optionally, the quantum dots  2101  and the quantum dots  2102  may be mixed at a predetermined proportion, such that the light-emitting elements composed of the blue light LED and the green light QDs and the red light QDs emits lights of three primary colors (red, green, blue), of which intensities are at a proportion of about 3:6:1. Standard white light can also be generated by the mixture with this proportion. 
     In the abovementioned exemplary embodiment, adoption of the luminescent solution of “monochromatic LED+quantum dots”, especially of “blue light LED+green light and red light QDs”, not only can generate standard white light, but also can provide colour gamut. 
     In another exemplary embodiment of the present disclosure, the front light source  200  may adopt a luminescent solution of “monochromatic LED+fluorescent powders”. In one example, each light source element  204  may comprise an LED emitting blue light and fluorescent powders emitting yellow light. In another example, each light source element  204  may comprise an LED emitting (near)ultraviolet light and fluorescent powders emitting RGB colored light. Principles and constructions of the monochromatic LED and the fluorescent powders are similar to those of conventional light source, and are not described for the sake of brevity herein. 
     In one example, referring to  FIG. 3 , the plurality of light source elements  204  are provided in array on the transparent substrate  202 , and pitches P between every two adjacent light source elements  204  are configured so that a light emitted by the front light source is uniformly distributed. In one example, the pitches P between every two adjacent light source elements  204  are the same. It is found in experiments that, when the pitches P are smaller than for example 1 millimeter, shadow of the light source element  204  is apparently visible; and when the pitches P are greater than for example 2.5 millimeters, production cost of the front light source  200  is increased obviously. Accordingly, in embodiments of the present disclosure, the pitches P are in the range of 1 millimeter˜2.5 millimeters. Relationship between the pitches P and light distribution will be further described in detail hereinafter. 
     In one example, a blue light LED as the light source element may have a size L S  of 6 microns˜30 microns in the X direction. In one example, the blue light LED may be transferred to the transparent substrate formed with the quantum dot elements by processes including transfer printing. 
     In one example, the light absorbing elements  206  and the LEDs  204  are in a one-to-one correspondence, and each light absorbing element  206  and one of the LEDs  204  corresponding to the each light absorbing element  206  form a single unit that may be customized in an LED manufacturer and be provided directly by the LED manufacturer. In another example, each light absorbing element  206  and one of the LEDs  204  corresponding to the each light absorbing element  206  may be formed independently from each other. For instance, a plurality of light absorbing elements  206  are formed on the transparent substrate  202  formed with the LEDs  204 , by a patterning process or an ink-jet printing process. 
     Further referring to  FIG. 3 , the front light source  200  may further comprise connection lines  212  configured for being electrically connected to the plurality of light source elements  204 . The connection lines  212  are provided on the transparent substrate  202 , and the connection lines  212  are electrically connected to the plurality of light source elements  204  arranged in array. In one example, a material for the connection line  212  may comprise transparent material including an ITO or an IZO. In this example, since the connection line is transparent, a line width of the connection line  212  may be relatively large, such as greater than or equal to 30 microns. In another example, the material for the connection line  212  may comprise a metal. In this example, since the connection line is non-transparent, a line width of the connection line  212  is generally relatively small, for instance, less than or equal to 3 microns, and the connection line  212  may be treated with surface oxidation to reduce reflectivity. As a result, the light emitted by the light source  204  is not reflected by the connection line  212  towards the front side, ensuring one-sided outgoing of the light, thereby further increasing the contrast. 
     Referring back to  FIG. 2 , the front light source  200  may further comprise a plurality of reflecting elements  214 . The plurality of reflecting elements  214  and the plurality of light source elements  204  are in a one-to-one correspondence. Each reflecting element  214  is provided between the light source element  204  and the light absorbing element  206  corresponding to the each reflecting element  214 , in order to reflect light emitted by each light source element  204  towards a direction away from the light absorbing element  206 , thereby further increasing one-sided outgoing effect of the light. In one example, a size of the reflecting element  214  in the X direction may be approximately equal to that of one of the light absorbing elements  206  corresponding to the reflecting element  214  in the X direction. It should be noted that, in some other embodiments, a front light source may comprise a plurality of reflecting elements, instead of comprising a plurality of light absorbing elements. Specifically, the plurality of reflecting elements are provided at front sides of a plurality of light source elements. The plurality of reflecting elements and the plurality of light source elements are in a one-to-one correspondence. An orthographic projection of each of the light source elements onto the transparent substrate is within an orthographic projection of one of the reflecting elements corresponding to the light source element onto the transparent substrate, and an area of the orthographic projection of the each of the light source elements onto the transparent substrate is smaller than an area of the orthographic projection of the one of the reflecting elements corresponding to the each light source element onto the transparent substrate. With this structure, a light emitted by each light source element is also reflected towards a direction away from the light absorbing element, thereby increasing one-sided outgoing effect of the light. 
     According to another aspect of embodiments of the present disclosure, there is provided a display device. Referring to  FIG. 4 , the display device  400  may comprise: the abovementioned front light source  200 ; and a display panel  410  provided at a rear side of the front light source  200 , wherein a reflecting component  4102  is provided at a side of the display panel  410  away from the front light source  200 . 
     In one example, the reflecting component  4102  may comprise a reflecting surface or a reflecting sheet. The reflecting component may be integrally formed with the display panel  410 , or, the reflecting component may be formed independently from the display panel  410  and then is bonded to the display panel  410  by means of adhesive and the likes. 
     Referring to  FIG. 3  and  FIG. 4 , the plurality of light source elements  204  are provided in array on the transparent substrate  202 , and pitches P between every two adjacent light source elements  204  are configured so that a light emitted by the front light source is uniformly distributed. In one example, the pitches P between every two adjacent light source elements  204  are the same, and the pitches P are in the range of 1 millimeter˜2.5 millimeters. 
     In one example, ratios of a distance D 2  between each light source element  204  and the reflecting surface or the reflecting sheet  4102  of the display panel  410  in a direction perpendicular to the display panel (namely Z direction in  FIG. 4 ) to the pitches P between every two adjacent light source elements are in the range of 1:1˜1:1.5. In an alternative example, ratios of a distance D 3  between each quantum dot element  210  and the reflecting surface or the reflecting sheet  4102  of the display panel  410  in the direction perpendicular to the display panel (namely the Z direction in  FIG. 4 ) to the pitches P between every two adjacent light source elements are in the range of 1:1˜1:1.5. Herein, the distance D 2  or the distance D 3  may be regarded as “light-mixing distance”. 
     In one example, the quantum dot element  210  has a size L QD  of about 70 μm in the X direction, the light-mixing distance D 3  is about 1.5 millimeters, and the pitch P is about 2.0 millimeters.  FIG. 5  shows a simulation diagram of optical distribution of the display device with the above design values. In  FIG. 5 , coordinates X, Y represent respectively coordinates of different data points in a simulation model. In this simulation experiment, uniformity of optical distribution can be up to 97.7%. 
     In the above example, a uniform light-mixing effect can be achieved by designating the pitch P and ratio relationship between the light-mixing distance and the pitch P. Thereby, uniformity of light emission of the front light source is increased, and the display effect of the display device is increased. 
     According to embodiments of the present disclosure, the abovementioned display device may comprise but not limited to any of products or components having a display function, including electronic paper, mobile phone, tablet computer, TV, displayer, notebook computer, digital photo frame, navigator and the likes. 
     In one example, a size of the display device is less than or equal to 8 inches. In this example, a material for the connection line  212  may be selected from transparent materials including an ITO or an IZO. In this way, a line width of the connection line may be relatively large, such as greater than or equal to 30 microns. 
     In another example, the size of the display device is greater than 8 inches. In this example, the material for the connection line  212  may comprise a metal, in order to avoid excessive voltage drop occurred in wirings of longer connection lines from affecting uniformity of optical distribution. In this example, since the connection line is non-transparent, a line width of the connection line  212  is generally relatively small, for instance, less than or equal to 3 microns, and the connection line  212  may be treated with surface oxidation to reduce reflectivity. As a result, the light emitted by the light source  204  is not reflected by the connection line  212  towards the front side, ensuring one-sided outgoing of the light, thereby further increasing the contrast. 
     Although some embodiments according to the general inventive concept of the present disclosure have been shown and described, it will be apparent, however, for those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept of the present disclosure, the scope of which is defined in the claims and their equivalents.