Patent Publication Number: US-9841632-B2

Title: Liquid crystal display panel, composite substrate and method for fabricating the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority to Chinese Patent Application No. 201510373281.X, titled “LIQUID CRYSTAL DISPLAY PANEL, COMPOSITE SUBSTRATE AND METHOD FOR FABRICATING THE SAME”, filed on Jun. 30, 2015 with the State Intellectual Property Office of the People&#39;s Republic of China, the content of which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present disclosure relates to the technical field of display devices, and in particular, to a liquid crystal display panel, and a composite substrate and a method for fabricating the composite substrate. 
     BACKGROUND OF THE INVENTION 
     At present, liquid crystal display, as one of mainstream display devices, is widely applied in various electronic products and is a necessary tool in people&#39;s work and daily life, since it has advantages such as ultrathin, displayable with a large-sized panel, a low power consumption, non-radiation and a high resolution. 
       FIG. 1  is a schematic structural diagram of a conventional liquid crystal display. The liquid crystal display includes: a TFT array substrate  11  and a color filter substrate  12  arranged opposite to each other; and a liquid crystal layer  13  arranged between the TFT array substrate  11  and the color filter substrate  12 . 
     In the conventional liquid crystal display, in order to ensure a normal image display, an alignment layer is arranged on a side of the TFT array substrate  11  close to the liquid crystal layer, so that a liquid crystal molecule M has an initial deflection angle. Moreover, a polarizer is arranged on a side of the TFT array substrate  11  far away from the liquid crystal layer, to selectively pass a linearly polarized light. 
     As can be seen, in the conventional TFT array substrate, two separate structures are necessary to serve as an alignment layer and a polarizer respectively, which results in a complex structure and a high fabrication cost. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to address the above issues, a liquid crystal display panel, and a composite substrate and a method for fabricating the composite substrate are provided according to embodiments of the present disclosure, so as to simplify the structure and fabrication cost of a TFT array substrate. 
     In order to achieve the above object, the present disclosure provides technical solutions as follows. 
     A composite substrate includes: a substrate, a carbon nanotube layer, a polarizing material and a photoalignment matrix material, 
     where the carbon nanotube layer is adhered to a surface of the substrate with the photoalignment matrix material; the carbon nanotube layer includes multiple carbon nanotubes extending in a same direction; the polarizing material is mixed into the photoalignment matrix material, and a molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. 
     A liquid crystal display panel is further provided according to the present disclosure, The liquid crystal display panel includes: a TFT array substrate and a color filter substrate arranged opposite to each other; and a liquid crystal layer arranged between the TFT array substrate and the color filter substrate; and the liquid crystal display panel further includes: a polarizing material, a photoalignment matrix material and a carbon nanotube layer, 
     wherein the carbon nanotube layer is adhered, with the photoalignment matrix material, to a surface of the TFT array substrate and/or a surface of the color filter substrate which are close to the liquid crystal layer; the polarizing material is mixed into the photoalignment matrix material; the photoalignment matrix material is adhered to the surface of the TFT array substrate and/or the surface of the color filter substrate which are close to the liquid crystal layer; the carbon nanotube layer includes multiple carbon nanotubes extending in a same direction; A molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. 
     A method for fabricating the above-described composite substrate is further provided according to the present disclosure. The method includes 
     preparing the substrate; 
     coating the substrate with the photoalignment matrix material mixed with the polarizing material; 
     laying the carbon nanotube layer on the surface of the photoalignment matrix material, the carbon nanotube layer including multiple carbon nanotubes extending in a same direction; and 
     solidifying the photoalignment matrix material to adhere the carbon nanotube layer to a surface of the substrate, where a molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. 
     It can be seen from the above description that the composite substrate according to the present disclosure includes: the substrate, the carbon nanotube layer arranged on the surface of the substrate, the polarizing material and the photoalignment matrix material. The carbon nanotube layer is adhered to the surface of the substrate with the photoalignment matrix material. The carbon nanotube layer includes multiple carbon nanotubes extending in the same direction. The polarizing material, of which the molecule arrangement direction is the same as the extending direction of the carbon nanotube, is mixed into the photoalignment matrix material. 
     Since the multiple carbon nanotubes of the carbon nanotube layer extend in the same direction, multiple grooves arranged in parallel may be formed between the carbon nanotubes arranged in parallel. The groove may be used for an initial alignment of the liquid crystal molecule, that is, the carbon nanotube layer may serve as an alignment layer. In addition, the carbon nanotube has a polarizing feature, to transmit a light of which a polarization direction is perpendicular to the extending direction of the carbon nanotube and absorb a light of which a polarization direction is parallel to the extending direction of the carbon nanotube, that is, the carbon nanotube layer may serve as a polarizing layer. Furthermore, the polarizing material, of which the molecule arrangement direction is the same as the extending direction of the carbon nanotube, is mixed into the photoalignment matrix material, thereby significantly enhancing a polarizing performance of the composite substrate. 
     As can be seen, the composite substrate may serve as both an alignment layer and a polarizing layer. A polarizing feature may be improved by adhering the carbon nanotube layer to a transparent substrate with the photoalignment matrix material, without an additional adhesive. Moreover, in a case that the composite substrate serves as a TFT array substrate and a color filter substrate, it is unnecessary to prepare the polarizing layer and the alignment layer separately, which leads to a simple structure and a low cost. 
     The liquid crystal display panel according to the present disclosure has a simple structure and a low fabrication cost since the composite substrate serves as the TFT array substrate and/or the color filter substrate. With the method for fabricating the composite substrate according to the present disclosure, the composite substrate may be prepared with a simple procedure and a low cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings to be used in the description of embodiments of the disclosure or the conventional technology are described briefly as follows, so that the technical solutions according to the embodiments of the present disclosure or according to the conventional technology may become clearer. It is apparent that the drawings referred in the following description only illustrate some embodiments of the present disclosure. For those skilled in the art, other drawings may be obtained according to these drawings without any creative work. 
         FIG. 1  is a schematic structural diagram of a conventional liquid crystal display; 
         FIG. 2  is a schematic structural diagram of a composite substrate according to an embodiment of the present disclosure; 
         FIG. 3  is a sectional diagram of the composite substrate shown in  FIG. 2  in a direction perpendicular to an extending direction of carbon nanotube; 
         FIG. 4  is a schematic structural diagram of a carbon nanotube film under a microscope; 
         FIG. 5  is a schematic structural diagram of a liquid crystal display panel according to an embodiment of the present disclosure; 
         FIG. 6  is a schematic structural diagram of a liquid crystal display panel according to an embodiment of the present disclosure; 
         FIG. 7  is a schematic structural diagram of a liquid crystal display panel according to an embodiment of the present disclosure; and 
         FIG. 8  is a flowchart of a method for fabricating the composite substrate according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical solutions according to embodiments of the present disclosure are described clearly and completely as follows in conjunction with the drawings hereinafter. It is apparent that the described embodiments are only a few rather than all of the embodiments according to the present disclosure. Any other embodiments obtained by those skilled in the art based on the embodiments in the present disclosure without any creative work fall into the scope of the present disclosure. 
     In a conventional liquid crystal display, each of a TFT array substrate and a color filter substrate has an alignment layer and a polarizer. The alignment layer and the polarizer are separately prepared for both the TFT array substrate and the color filter substrate. In manufacture process, an alignment layer is rubbed to be aligned after being formed. In a fabrication of a polarizer, a multi-layer structure of the polarizer is prepared, which results in a more complex procedure and a higher fabrication cost. The polarizer generally includes a polarizing layer, a TAC (poly cellulose triacetate) layer, an adhesive layer, a release film, a protective film and a reflecting film. 
     It is found that both the alignment layer and the polarizer may be achieved with the carbon nanotube layer, thereby addressing the issues of a complex structure and a high fabrication cost since the alignment layer and the polarizer are prepared separately on TFT array substrate and the conventional color filter substrate in the conventional technology. 
     Based on the above, a composite substrate is provided according to an embodiment of the present disclosure, referring to  FIG. 2  and  FIG. 3 .  FIG. 2  is a schematic structural diagram of a composite substrate according to an embodiment of the present disclosure, and  FIG. 3  is a sectional diagram of the composite substrate shown in  FIG. 2  in a direction perpendicular to the extending direction of carbon nanotube. 
     The composite substrate includes a substrate  21 , a carbon nanotube layer  23  arranged on a surface of the substrate  21 , a photoalignment matrix material  22  and a polarizing material  24 . The carbon nanotube layer  23  is adhered to a surface of the substrate  21  with the photoalignment matrix material  22 . The carbon nanotube layer  23  includes multiple carbon nanotubes extending in a same direction. The polarizing material  24 , of which a molecule arrangement direction is the same as the extending direction of the carbon nanotube, is mixed into the photoalignment matrix material  22 . 
     The substrate  21  mainly serves as a support, and may be made of a flexible or hard transparent material, such as glass, quartz, diamond or plastic. In the embodiment, the substrate  21  may be a glass plate. Optionally, the substrate  21  may be a TFT array substrate, a color filter substrate or other structures of a liquid crystal display panel. 
     The carbon nanotube layer  23  includes at least one layer of carbon nanotube film. The carbon nanotube film may be a self-supported film structure directly pulled from a carbon nanotube array. The “self-supported film structure” means that the carbon nanotube film can be hanged to maintain its film state by supporting forces provided by only two opposite edges, without a large area supporter. 
       FIG. 4  is a schematic structural diagram of a carbon nanotube film under a microscope. The carbon nanotube film includes multiple carbon nanotubes preferably orientated in a same direction and arranged parallel to a surface of the carbon nanotube film. Each carbon nanotube is end-to-end connected to a neighbor carbon nanotube in the extending direction of the carbon nanotube via van der Waals forces and is tightly connected to a neighbor carbon nanotube in a direction perpendicular to the extending direction of the carbon nanotube via van der Waals forces, to form a continuous self-supported film structure. 
     Since the carbon nanotubes of the carbon nanotube film extend in the same direction, multiple grooves extending in the same direction may be formed between the carbon nanotubes arranged in parallel. The groove may be used for an initial alignment of liquid crystal molecules. The carbon nanotube film has a thickness in a range between 0.5 nm and 100 μm, a width of the carbon nanotube film depends on a size of the carbon nanotube array from which the carbon nanotube film is pulled, and a length of the carbon nanotube film is not limited. 
     The carbon nanotube film has a good transparence, and a light transmittance of the carbon nanotube film may be above 80%, since the carbon nanotube film has a small thickness. After the carbon nanotube film is thinned by a laser, the light transmittance of the carbon nanotube film may be above 90%. Therefore, the carbon nanotube film of the carbon nanotube layer according to an embodiment of the present disclosure is a laser-thinned carbon nanotube film, hence the carbon nanotube layer has a high light transmittance. 
     In addition, since the carbon nanotubes of the carbon nanotube film extend in the same direction, the carbon nanotube film is resistivity anisotropic, that is, the carbon nanotube film has a minimal resistance in the extending direction of the carbon nanotube and has a maximal resistance in a direction perpendicular to the extending direction of the carbon nanotube. The sheet resistance of the carbon nanotube film in a direction perpendicular to the extending direction of the carbon nanotube is more than ten times the sheet resistance of the carbon nanotube film in a direction parallel to the extending direction of the carbon nanotube. 
     Moreover, referring to  FIG. 2 , the carbon nanotubes have a polarizing feature, to transmit a light of which a polarization direction is perpendicular to the extending direction of the carbon nanotube and absorb a light of which a polarization direction is parallel to the extending direction of the carbon nanotube. Therefore, the carbon nanotube film has a polarizing feature, hence the composite substrate has the polarizing feature and may serve as a polarizing layer. 
     The carbon nanotubes may include one or more of a single-walled carbon nanotube, a double-walled carbon nanotube and a multi-walled carbon nanotube. The carbon nanotubes have a diameter in a range between 0.5 nm and 50 nm and the carbon nanotubes have a length in a range between 50 nm and 5 mm. Preferably, the carbon nanotubes have a length in a range between 100 μm and 900 μm. The carbon nanotubes may be laid in parallel without space to form a carbon nanotube layer  23  of a large area, or arranged in a stack manner to form a carbon nanotube layer  23  of a large thickness. As long as it is ensured that all carbon nanotubes of the carbon nanotube layer  23  extend in the same direction, any arrangement manner may be used. 
     In a case that only one layer of carbon nanotube film exists in the carbon nanotube layer  23 , the carbon nanotube film has a high light transmittance, a low fabrication cost and the carbon nanotube film is laid simply. Therefore, in an embodiment, the carbon nanotube layer  23  is preferably configured to include only one layer of carbon nanotube film. It should be noted that, one layer of carbon nanotube film may include multiple carbon nanotubes stacked in thickness, and the number of carbon nanotubes stacked at different locations are not necessarily the same. 
     In the composite substrate according to the embodiment, the photoalignment matrix material has a good photoalignment feature, and can generate a predetermined photoalignment orientation under an irradiation of ultraviolet light. Hence, the photoalignment matrix material  22  has a predetermined photoalignment orientation, thereby improving an alignment performance of the carbon nanotube layer  23 . 
     The alignment performance of the carbon nanotube layer  23  may be improved with the photoalignment matrix material  22 , in a case that an included angle between the alignment orientation of the photoalignment matrix material  22  and the extending direction of the carbon nanotube is in a range from 0 degree to 90 degrees, inclusively. The photoalignment matrix material  22  may have a predetermined photoalignment orientation in a case that the photoalignment matrix material  22  is irradiated by a polarized ultraviolet light, and the photoalignment orientation may be determined by controlling a polarization direction of the polarized ultraviolet light and energy of the polarized ultraviolet light. Optionally, in the embodiment of the present disclosure, the included angle between the photoalignment orientation of the photoalignment matrix material  22  and the extending direction of the carbon nanotube may be set to be 0 degree, to enhance the alignment performance of the carbon nanotube layer  23  maximally. 
     The photoalignment matrix material  22  is in a liquid state initially, and the carbon nanotube layer  23  may be partially or completely covered with the photoalignment matrix material  22 . In the embodiment referring to  FIG. 2  and  FIG. 3 , the carbon nanotube layer  23  is completely covered with the photoalignment matrix material  22 . After the photoalignment matrix material  22  is solidified, multiple grooves distributed uniformly may be formed on a surface of the photoalignment matrix material  22  due to the existence of grooves in the carbon nanotube layer. 
     The photoalignment matrix material  22  includes one or more materials of cellulose triacetate, polyimide and polyamic acid. In an embodiment, the photoalignment matrix material  22  is the polyimide. 
     In the composite substrate according to an embodiment of the present disclosure, the polarizing material is a dichroic organic dye. The dichroic organic dye includes one or more materials of an azoic dye, an anthraquinone dye, a biphenyl dye, triphenyl dioxazine and derivative dyes, a monomethine dye, a polymethine dye and a polycyclic dye. 
     The dichroic organic dye can be oriented under an irradiation of polarized ultraviolet light. Besides, due to dichroism of the dichroic organic dye, under an irradiation of natural light, the dichroic organic dye may transmit a light in one polarization direction and block a light in other directions. Hence, the dichroic organic dye has the same polarizing feature as that of a polarizer. In the composite substrate, the polarizing material  24  is a dichroic organic dye with a dichroic ratio larger than or equal to 7. In this case, the composite substrate has a good polarizing performance. 
     A structure of the azoic dichroic organic dye may be represented as: 
     
       
         
         
             
             
         
       
     
     where an R group connected to an N atom in (3) may be: 
     
       
         
         
             
             
         
       
     
     Furthermore, the polarizing material may further comprise materials with structures of benzidine, diphenylureas, stilbenes, dinaphthyl amines, J-acids or anthraquinones, to improve the polarizing performance. 
     Optionally, an electron donating group/electron withdrawing group may be adsorbed on an end of a molecule (preferably a terminal of the molecule) of the dichroic organic dye. A precision of polarized light in a composite substrate region may be improved and the composite substrate has a better stability since the dichroism of the dichroic organic dye is increased by introducing the electron donating group/electron withdrawing group. In a case that the dichroic organic dye with the dichroism ratio larger than or equal to 7 is used, the polarizing performance of the composite substrate is optimal if a direction in which molecules of the dichroic organic dye is the same as the extending direction of the carbon nanotube. 
     Referring to  FIG. 2  and  FIG. 3 , in the composite substrate, the photoalignment matrix material  22  is in a liquid state initially, and penetrates into spaces between adjacent carbon nanotubes. A surface of the carbon nanotube layer  23  far away from the substrate  21  is covered with the photoalignment matrix material  22 . After the photoalignment matrix material  22  is solidified, multiple grooves are formed on the surface of the photoalignment matrix material  22  far away from the substrate  21 , and an extending direction of the groove is parallel to the extending direction of the carbon nanotube. In this case, after the photoalignment matrix material  22  is solidified, a microstructure of the surface of the photoalignment matrix material  22  may be the same as a microstructure of the carbon nanotube layer, and the photoalignment matrix material  22  may be cooperated with the carbon nanotube layer  23 , thereby significantly improving the alignment performance of the carbon nanotube layer  23 . 
     The composite substrate according to the embodiment of the present disclosure has advantages as follows. Since the carbon nanotube layer  23  has a regular microstructure and is modified with the photoalignment matrix material  22 , the composite substrate may have a good alignment performance and may be adhered to a surface of an element with the photoalignment matrix material  22  without an additional adhesive. The carbon nanotube layer  23  has a good electrical conductivity, a good light transmittance and a good polarizing performance. Accordingly, the composite substrate also has the above-described performances, and may serve as an alignment layer, a polarizer or other structures such as a transparent electrode. Moreover, the polarizing performance of the composite substrate is further enhanced since the polarizing material is mixed into the photoalignment matrix material. It can be seen from the above description that, the composite substrate according to the embodiment of the present disclosure has a polarizing feature and an alignment feature, and may serve as a polarizer and an alignment layer. In a case that the substrate of the composite substrate is a TFT array substrate, the TFT array substrate may serve as a polarizer and an alignment layer, hence the TFT array substrate has a simpler structure and lower fabrication cost compared with the conventional TFT array substrate for which the polarizer and the alignment layer are prepared separately. 
     In a case that the substrate of the composite substrate is a color filter substrate, the color filter substrate may serve as a polarizer and an alignment layer, and hence the color filter substrate has a simpler structure and a lower fabrication cost compared with a conventional color filter substrate for which a polarizer and an alignment layer are prepared separately. Since the alignment layer and the polarizer for the composite substrate are integrated into one structure, the thickness and fabrication cost of a liquid crystal display panel may be reduced significantly if the composite substrate is used for preparing the liquid crystal display panel. 
     The carbon nanotube layer may be adhered to a transparent substrate with the photoalignment matrix material without an additional adhesive, which results in a further improved polarizing feature, a simple structure and a low cost. 
     Based on the composite substrate according to the above-described embodiment, a liquid crystal display panel is further provided according to an embodiment of the present disclosure. The liquid crystal display panel includes: a TFT array substrate and a color filter substrate arranged opposite to each other; and a liquid crystal layer arranged between the TFT array substrate and the color filter substrate; and the liquid crystal display panel further includes: a polarizing material, a photoalignment matrix material and a carbon nanotube layer. The carbon nanotube layer is adhered, with the photoalignment matrix material, to a surface of the TFT array substrate and/or a surface of the color filter substrate which are close to the liquid crystal layer; the polarizing material is mixed into the photoalignment matrix material; the photoalignment matrix material is adhered to the surface of the TFT array substrate and/or the surface of the color filter substrate which are close to the liquid crystal layer; the carbon nanotube layer includes multiple carbon nanotubes extending in a same direction; the polarizing material is mixed into the photoalignment matrix material and a molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. 
     An alignment direction of the TFT array substrate is perpendicular to an alignment direction of the color filter substrate, and a light polarization direction of the TFT array substrate is perpendicular to a light polarization direction of the color filter substrate. 
     A structure of the TFT array substrate may be set to be the structure of the composite substrate according to the above-described embodiment, and a structure of a conventional color filter structure is applied to the color filter substrate. That is, the carbon nanotube layer, the polarizing material and the photoalignment matrix material are arranged on only a surface of the TFT array substrate close to the liquid crystal layer, a conventional polarizer is prepared on a surface of the color filter substrate far away from the liquid crystal layer and a conventional alignment layer is prepared on a surface of the color filter substrate close to the liquid crystal layer. In this case, the structure of the liquid crystal display panel is shown in  FIG. 5 . 
       FIG. 5  is a schematic structural diagram of a liquid crystal display panel according to an embodiment of the present disclosure. The liquid crystal display panel includes: a TFT array substrate a 1  and a color filter substrate  52  arranged opposite to each other; and a liquid crystal layer  53  arranged between the TFT array substrate a 1  and the color filter substrate  52 . 
     In the embodiment referring to  FIG. 5 , the color filtercolor filter substrate  52  may have a structure of a conventional color filtercolor filter substrate. A photoalignment matrix material a 2  and a carbon nanotube layer a 3  are arranged on a surface of the TFT array substrate a 1  close to the liquid crystal layer  53 . A polarizing material a 4 , of which a molecule arrangement direction is the same as the extending direction of the carbon nanotube, is mixed into the photoalignment matrix material a 2  to enhance a polarizing performance of the TFT array substrate. 
     In the liquid crystal display panel shown in  FIG. 5 , the alignment layer and polarizer on the surface of the TFT array substrate a 1  may be replaced by the carbon nanotube layer a 3  and the photoalignment matrix material a 2 , thereby simplifying the structure of the TFT array substrate a 1 , which leads to a simple fabrication procedure and a low cost. An Indium Tin Oxide (ITO) layer is formed to serve as a common electrode layer in a conventional TFT array substrate. In the embodiment of the present disclosure, since the carbon nanotube layer a 3  has a good electrical conductivity in a direction parallel to the extending direction of the carbon nanotube, a common voltage may be input to the carbon nanotube layer a 3  of the TFT array substrate a 1 , and the carbon nanotube layer a 3  of the TFT array substrate a 1  may serve as the common electrode layer. In this case, the structure of the TFT array substrate is simplified and the fabrication cost of the TFT array substrate is reduced since it is unnecessary to separately prepare a common electrode layer on the TFT array substrate. 
     In the liquid crystal display panel according to the embodiment of the present disclosure, the structure of the TFT array substrate may also be set to be a structure of a conventional TFT array substrate, and the composite substrate according to the above-described embodiment serves as the color filter substrate. In this case, the structure of the liquid crystal display panel is shown in  FIG. 6 . 
       FIG. 6  is a schematic structural diagram of a liquid crystal display panel according to an embodiment of the present disclosure. The liquid crystal display panel includes: a TFT array substrate  61  and a color filter substrate b 1  arranged opposite to each other; and a liquid crystal layer  63  arranged between the TFT array substrate  61  and the color filter substrate b 1 . 
     In an embodiment referring to  FIG. 6 , a structure of the TFT array substrate  61  may be a structure of a conventional TFT array substrate. A photoalignment matrix material b 2  and a carbon nanotube layer b 3  are arranged on a surface of the color filter substrate b 1  close to the liquid crystal layer  63 . A polarizing material b 4 , of which a molecule arrangement direction is the same as the extending direction of the carbon nanotube, is mixed into the photoalignment matrix material b 2  to enhance a polarizing performance of the color filter substrate b 1 . 
     In the liquid crystal display panel shown in  FIG. 6 , the alignment layer and the polarizer on the surface of the color filter substrate b 1  may be replaced by the carbon nanotube layer b 3  and the photoalignment matrix material b 2 , thereby simplifying the structure of the color filter substrate, which leads to a simple fabrication procedure and a low cost. An ITO layer is formed to serve as a shielding electrode layer in a conventional color filter substrate. In the embodiment of the present disclosure, since the carbon nanotube layer b 3  has a good electrical conductivity in a direction parallel to the extending direction of the carbon nanotube, the carbon nanotube layer b 3  on the surface of the color filter substrate b 1  may be grounded and may serve as a shielding electrode layer. In this case, the structure of the color filter structure is further simplified and the fabrication cost of the color filter substrate is reduced since it is unnecessary to separately prepare the shielding electrode layer on the color filter substrate. 
     A carbon nanotube layer and a photoalignment matrix material mixed with a polarizing material may be arranged on a surface of the TFT array substrate and a surface of the color filter substrate. In this case, the carbon nanotube layer of the liquid crystal display panel includes a first carbon nanotube layer arranged on the surface of the TFT array substrate and a second carbon nanotube layer arranged on the surface of the color filter substrate. The photoalignment matrix material includes a first photoalignment matrix material layer arranged on the surface of the TFT array substrate and a second photoalignment matrix material layer arranged on the surface of the color filter substrate. The structure of the liquid crystal display panel is shown in  FIG. 7 . 
       FIG. 7  is a schematic structural diagram of a liquid crystal display panel according to an embodiment of the present disclosure. The liquid crystal display panel includes: a TFT array substrate c 1  and a color filter substrate d 1  arranged opposite to each other; and a liquid crystal layer  73  arranged between the TFT array substrate c 1  and the color filter substrate d 1 . 
     In the embodiment referring to  FIG. 7 , a first photoalignment matrix material layer c 2  and a first carbon nanotube layer c 3  are arranged on a surface of the TFT array substrate c 1  close to the liquid crystal layer  73 . A second photoalignment matrix material layer d 2  and a second carbon nanotube layer d 3  are arranged on a surface of the color filter substrate d 1  close to the liquid crystal layer  73 . An extending direction of the carbon nanotube of the TFT array substrate c 1  is perpendicular to an extending direction of the carbon nanotube of the color filter substrate d 1 , so that an alignment direction of the TFT array substrate c 1  is perpendicular to an alignment direction of the color filter substrate d 1 , and a light polarization direction of the TFT array substrate c 1  is perpendicular to a light polarization direction of the color filter substrate d 1 . A polarizing material c 4 , of which a molecule arrangement direction is the same as the extending direction of the carbon nanotube of the first carbon nanotube layer c 3 , is mixed into the first photoalignment matrix material layer c 2  to enhance a polarizing performance of the TFT array substrate c 1 . A polarizing material d 4 , of which a molecule arrangement direction is the same as the extending direction of the carbon nanotube of the second carbon nanotube layer d 3 , is mixed into the second photoalignment matrix material layer d 2  to enhance a polarizing performance of the color filter substrate d 1 . 
     In the liquid crystal display panel as shown in  FIG. 7 , the alignment layer and the polarizer on the surface of the TFT array substrate c 1  may be replaced by the first carbon nanotube layer c 3  and the first photoalignment matrix material layer c 2 , and the alignment layer and the polarizer on the surface of the color filter substrate d 1  may be replaced by the second carbon nanotube layer d 3  and the second photoalignment matrix material layer d 2 , thereby simplifying structures of the color filter substrate d 1  and TFT array substrate c 1 , which leads to a simple fabrication procedure and a low cost. In a conventional TFT array substrate, an ITO layer is formed to serve as a common electrode layer. In  FIG. 7 , since the first carbon nanotube layer c 3  has a good electrical conductivity in a direction parallel to the extending direction of the carbon nanotube, a common voltage may be input to the first carbon nanotube layer c 3  of the TFT array substrate c 1 , and the first carbon nanotube layer c 3  of the TFT array substrate c 1  may serve as a common electrode layer. In this case, it is unnecessary to separately prepare the common electrode layer on the TFT array substrate, thereby further simplifying the structure of the TFT array substrate and reducing the fabrication cost of the TFT array substrate. For a conventional color filter substrate, an ITO layer is formed to serve as a shielding electrode layer. In  FIG. 7 , since the second carbon nanotube layer d 3  has a good electrical conductivity in a direction parallel to the extending direction of the carbon nanotube, the second carbon nanotube layer d 3  of the color filter substrate d 1  may be grounded and may serve as a shielding electrode layer. In this case, it is unnecessary to separately prepare the shielding electrode layer on the color filter substrate, thereby further simplifying the structure of the color filter substrate and reducing the fabrication cost of the color filter substrate. 
     In the embodiment of the present disclosure, in a case that the carbon nanotube layer of the composite substrate serves as a shielding electrode layer or a common electrode layer, special routes are arranged so as to ground the carbon nanotube layer or input the common voltage to the carbon nanotube layer. 
     A method for fabricating the composite substrate according to the above-described embodiments is further provided according to an embodiment of the present disclosure.  FIG. 8  is a flowchart of a method for fabricating the composite substrate according to an embodiment of the present disclosure, and the fabrication method includes steps S 11  to S 14 . 
     In step S 11 , a substrate is prepared. 
     The substrate mainly serves as a supporter and may be made of a flexible or hard transparent material, such as glass, quartz, diamond or plastic. In an embodiment, the substrate is a glass plate. It is to be understood that, the substrate may also be a TFT array substrate, a color filter substrate or other structures of a liquid crystal display device. 
     In step S 12 , the substrate is coated with a photoalignment matrix material mixed with a polarizing material. 
     The photoalignment matrix material includes one or more materials of cellulose triacetate, polyimide and polyamic acid. The photoalignment matrix material is in a liquid state initially and the photoalignment matrix material, after being irradiated by a light, aligned and solidified, may be used for adhering and fixing the carbon nanotube layer. 
     A surface of the substrate may be coated uniformly with a solution of the photoalignment matrix material by whirl coating or spin-coating. A thickness of the coating may be selected as needed. Preferably, the thickness of the coating is in a range between 100 nm and 100 μm. 
     In step S 13 , a carbon nanotube layer is laid on a surface of the photoalignment matrix material, and the carbon nanotube layer includes multiple carbon nanotubes extending in a same direction. 
     The carbon nanotube layer is completely or partially immersed in the coating. If the carbon nanotube layer serves as a common electrode layer or a shielding electrode layer, routes are arranged for the carbon nanotube layer in the step. 
     The step may further include a step of pre-baking the photoalignment matrix material in the liquid state, to remove an excess solvent in the photoalignment matrix material to facilitate the subsequent photoalignment and solidification. Optionally, a temperature for the pre-baking may be in a range between 90 degrees Celsius and 130 degrees Celsius, and a duration for the pre-baking may be in a range between 60 s and 120 s. In an embodiment, the temperature for the pre-bake is approximately 130 degrees Celsius and the duration for the pre-bake is approximately 120 s. 
     In step S 14 , the photoalignment matrix material is solidified to adhere the carbon nanotube layer to the surface of the substrate, and a molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. 
     In the step, the solidifying the photoalignment matrix material includes: irradiating the photoalignment matrix material with a polarized ultraviolet light, where the photoalignment matrix material is solidified to have a predetermined photoalignment orientation, and the molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. An included angle between the photoalignment orientation and the extending direction of the carbon nanotube is in a range from 0 degree to 90 degrees, inclusively. Optionally, the included angle is set to be 0 degree, thereby optimizing the alignment performance and polarizing performance of the composite substrate. 
     The photoalignment matrix material may be oriented under an irradiation of the polarized ultraviolet light. Energy of the polarized ultraviolet light may be in a range between 300 mJ and 1000 mJ, or optionally may be in a range between 500 mJ and 800 mJ. In the embodiment of the present disclosure, preferably, a polyimide film serves as the photoalignment matrix material. In a case of the above-described irradiation energy, a photoalignment performance of the polyimide film is optimal. The included angle between the polarization direction of the polarized ultraviolet light and the extending direction of the carbon nanotube of the carbon nanotube layer may be optionally 0 degree by adjusting the polarization direction of the polarized ultraviolet light. That is, the polarization direction of the polarized ultraviolet light is parallel to the extending direction of the carbon nanotube of the carbon nanotube layer. In this case, the photoalignment matrix material is oriented in a direction parallel to the extending direction of the carbon nanotube, an included angle between the photoalignment orientation and the extending direction of the carbon nanotube equals to 0 degree, and the molecule arrangement direction of the polarizing material is the same as the extending direction of the carbon nanotube. 
     After photoaligned by the polarized ultraviolet light, the photoalignment matrix material may be heated at a temperature in a range between 210 degrees Celsius and 230 degrees Celsius for 20 min to 50 min, to accelerate the solidification. In an embodiment, the temperature for the solidification is approximately 230 degrees Celsius and the duration for the solidification is approximately 30 min. 
     The fabrication method according to the embodiment of the present disclosure has advantages such as a simple process, a high production efficiency and facilitating a mass production. The above composite substrate may be prepared by using the fabrication method. 
     With the above descriptions of the disclosed embodiments, those skilled in the art may practice or use the present disclosure. Various modifications to the embodiments are apparent for those skilled in the art. The general principle suggested herein can be implemented in other embodiments without departing from the spirit or scope of the disclosure. Therefore, the present disclosure should not be limited to the embodiments disclosed herein, but has the widest scope that is conformity with the principle and the novel features disclosed herein.