Abstract:
Disclosed is a method for making a silicon quantum dot planar concentrating solar cell. At first, silicon nitride or silicon oxide mixed with silicon quantum dots is provided on a transparent substrate. By piling, there is formed a planar optical waveguide for concentrating sunlit into a small dot cast on a small solar cell.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for making a concentrating solar cell assembly and, more particularly, to a method for making a planar concentrating solar cell assembly with silicon quantum dots. 
       DESCRIPTION OF THE RELATED ARTS 
       [0002]    A typical solar cell assembly includes a solar cell, a Frenzel lens for focusing sunlit onto the solar cell and a sunlit-tracking unit for aligning the solar cell to the sun. The solar cell assembly is complicated and expensive. The maintenance of the solar cell is also expensive. Moreover, an optical waveguide material used in the solar cell assembly is a glass-based material, and the configuration is coaxial, and the size is big. Therefore, it is difficult for the solar cell assembly to fit in a building. 
         [0003]    The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an objective of the present invention to provide a method for making an inexpensive solar cell assembly. 
         [0005]    It is another objective of the present invention to provide a planar concentrating solar cell assembly that can easily fit in a building. 
         [0006]    To achieve the foregoing objectives, the method includes the step of providing a substrate with a refractive index larger than that of the air so that total reflection could occur at the interface between the substrate and the air. A silicon-quantum-dot film is provided on the substrate. The silicon-quantum-dot film contains silicon quantum dots. The thickness of the silicon-quantum-dot film is 0.1 to 100 micrometers, and the size of the silicon quantum dots is 1 to 10 nanometers. A silicon-oxide film is provided on the silicon-quantum-dot film so that the substrate, the silicon-quantum-dot film and the silicon-oxide film together form a planar optical waveguide. The thickness of the silicon-oxide film is 0.1 to 10 micrometers. A solar cell is arranged near the planar optical waveguide. In operation, sunlit is cast onto the silicon quantum dots so that they refract and diffract some of the sunlit and absorb some other sunlit and hence cast re-emitted light. The refracted or diffracted sunlit and the re-emitted light reflect from the interface because of total reflection and become totally reflected light that is focused and directed to the solar cell. 
         [0007]    In another aspect, the method comprises the steps of providing a substrate and providing a silicon-quantum-dot film on the substrate. The refractive index of the substrate is larger than that of the air so that total reflection could occur at the interface between the substrate and the air. The silicon-quantum-dot film contains silicon quantum dots. The thickness of the silicon-quantum-dot film is 0.1 to 100 micrometers, and the size of the silicon quantum dots is 1 to 10 nanometers. The two previous steps are repeated to provide optical units each comprising a substrate and a silicon-quantum-dot film. The optical units are piled. A silicon-oxide film is provided on the silicon-quantum-dot film of one of the optical units so that the optical units and the silicon-oxide film together form a planar optical waveguide. The thickness of the silicon-oxide film is 0.1 to 10 micrometers. A solar cell is arranged near the planar optical waveguide. In operation, sunlit is cast onto the silicon quantum dots of each of the optical units so that the silicon quantum dots refract and diffract some of the sunlit and absorb the other sunlit and hence cast re-emitted light. The refracted and diffracted sunlit and the re-emitted light reflect from the interface between the substrate of an optical unit and the silicon-quantum-dot film of an adjacent optical unit and the interface between the substrate and the air because of total reflection and become totally reflected light that is focused and directed to the solar cell. 
         [0008]    Other objectives, advantages and features of the present invention will become apparent from the following description referring to the attached drawings. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0009]    The present invention will be described via the detailed illustration of two embodiments referring to the drawings. 
           [0010]      FIG. 1  is a flow chart of a method for making a silicon-quantum-dot planar concentrating solar cell assembly with according to the first embodiment of the present invention. 
           [0011]      FIG. 2  is a cross-sectional view of a substrate used in the method shown in  FIG. 1 . 
           [0012]      FIG. 3  is a cross-sectional view of a silicon-quantum-dot layer on the substrate shown in  FIG. 2 . 
           [0013]      FIG. 4  is a cross-sectional view of a planar optical waveguide made by providing a silicon-oxide film on the silicon-quantum-dot layer shown in  FIG. 3 . 
           [0014]      FIG. 5  is a cross-sectional view of a silicon-quantum-dot planar concentrating solar cell assembly made by providing a solar cell near the planar optical waveguide shown in  FIG. 4 . 
           [0015]      FIG. 6  is a flow chart of a method for making a planar concentrating solar cell assembly with silicon quantum dots according to the second embodiment of the present invention. 
           [0016]      FIG. 7  is a cross-sectional view of optical units used in the method shown in  FIG. 6 . 
           [0017]      FIG. 8  is a cross-sectional view of a silicon-quantum-dot planar concentrating solar cell assembly made in the method shown in  FIG. 6 . 
           [0018]      FIG. 9  is an enlarged view of the planar optical waveguide shown in  FIG. 4 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring to  FIG. 1 , a method for making a silicon-quantum-dot planar concentrating solar cell assembly according to a first embodiment of the present invention is shown. 
         [0020]    Referring to  FIGS. 1 and 2 , at  11 , there is provided a substrate  20 . The substrate  20  is a transparent plate made of glass, plastics or resin. The refractive index of the substrate  20  is larger than that of the air so that total reflection could occur at the interface between the substrate  20  and the air. 
         [0021]    Referring to  FIGS. 1 and 3 , at  12 , a silicon-quantum-dot film is provided on the substrate  20  based on a physical or chemical method. The thickness of the silicon-quantum-dot film  21  is 0.1 to 100 micrometers. The silicon-quantum-dot film  21  includes silicon quantum dots  211  evenly distributed in silicon nitride or silicon oxide. The size of the silicon quantum dots  211  is 1 to 10 nanometers. 
         [0022]    Referring to  FIGS. 1 and 4 , at  13 , a silicon-oxide film  22  is provided on the silicon-quantum-dot film  21 . Thus, the substrate  20 , the silicon-quantum-dot film  21  and the silicon-oxide film  22  together form a planar optical waveguide  2 . The thickness of the silicon-oxide film  22  is 0.1 to 10 micrometers. 
         [0023]    Referring to  FIGS. 1 and 5 , at  14 , a solar cell  5  is arranged near the planar optical waveguide  2 . The area of the solar cell is identical to the area of a flank of the planar optical waveguide  2 . Thus, the solar cell  5  and the planar optical waveguide  2  together form a silicon-quantum-dot planar concentrating solar cell assembly  6 . 
         [0024]    Referring to  FIGS. 5 and 9 , in operation, sunlit  3  is cast onto the silicon quantum dots  211 . The silicon quantum dots  211  refract and diffract some of the sunlit  3  into refracted and diffracted sunlit  3   a . The silicon quantum dots  211  absorb the other sunlit  3  and therefore cast re-emitted light  3   b . The refracted and diffracted sunlit  3   a  reflects from the interface between the substrate  20  and the air because of total reflection and becomes totally reflected light  4   a . Similarly, the re-emitted light  3   b  reflects from the interface and become totally reflected light  4   b . The totally reflected light  4   a  and  4   b  is focused and directed to the solar cell  5  as indicated with “4.” 
         [0025]    The concentration ratio M of the silicon-quantum-dot planar concentrating solar cell assembly  6  is calculated as follows: 
         [0000]        M=A /(4 ×a ); 
         [0026]    wherein “A” represents the area of the substrate  20  towards the sun, and “a” stands for the area of a flank of the substrate  20 . 
         [0027]    The conversion efficiency n of the silicon-quantum-dot planar concentrating solar cell assembly  6  is determined as follows: 
         [0000]      η= P /( S×A );
 
         [0028]    wherein “P” represents the power of the silicon-quantum-dot planar concentrating solar cell assembly  6 , and “S” represents the power density of the sunlit, and “A” represents the area of the substrate  20  towards the sun. 
         [0029]    Referring to  FIG. 6 , a method for making a silicon-quantum-dot planar concentrating solar cell assembly according to a second embodiment of the present invention is shown. 
         [0030]    Referring to  FIGS. 6 and 7 , at  11   a , there is provided a substrate  20 . The substrate  20  is a transparent plate made of glass, plastics or resin. 
         [0031]    At  12   a , a silicon-quantum-dot film  21  is provided on the substrate  20  according to a physical or chemical method. The thickness of the silicon-quantum-dot film  21  is 0.1 to 100 micrometers. The silicon-quantum-dot film  21  includes silicon quantum dots  211  evenly distributed in silicon nitride or silicon oxide. The size of the silicon quantum dots  211  is 1 to 10 nanometers. 
         [0032]    At  13   a , the two foregoing steps are repeated for a predetermined number of times to provide the predetermined number of optical units each including a substrate  20  and a silicon-quantum-dot film  21 . The optical units are piled. Then, a silicon-oxide film  22  is provided on the silicon-quantum-dot film  21  of one of the optical units. Together, the substrate  20 , the silicon-quantum-dot film  21  and the silicon-oxide film  22  form a planar optical waveguide  2   a.    
         [0033]    Referring to  FIGS. 6 and 8 , at  14   a , a solar cell  5   a  is arranged near the planar optical waveguide  2   a . The area of the solar cell  5   a  is identical to the area of a flank of the planar optical waveguide  2   a . Together, the solar cell  5   a  and the planar optical waveguide  2   a  form a silicon-quantum-dot planar concentrating solar cell assembly  6   a.    
         [0034]    Sunlit  3  is cast onto the silicon quantum dots  211  of each of the optical units. The silicon quantum dots  211  refract and diffract some of the sunlit  3  into refracted and diffracted sunlit  3   a . The silicon quantum dots  211  absorb the other sunlit  3  and therefore cast re-emitted light  3   b . The refracted and diffracted sunlit  3   a  reflects from the interface between the substrate  20  of an optical unit and the silicon-quantum-dot film of an adjacent optical unit and the interface between the substrate  20  and the air because of total reflection and become totally reflected light  4   a . Similarly, the re-emitted light  3   b  reflects from the interface and becomes totally reflected light  4   b . The totally reflected light  4   a  and  4   b  is focused and directed to the solar cell  5  as indicated with “ 4 .” Each of the optical units focuses and directs some light to the solar cell  5   a.    
         [0035]    The silicon-quantum-dot planar concentrating solar cell assembly of the present invention exhibits several advantages. Firstly, it is made with a flat configuration so that it can easily fit in a building. Secondly, it is inexpensive because it is simple and without a light tracker. Thirdly, it is efficient. 
         [0036]    The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.