Abstract:
This invention discloses a thin-film solar cell, provided with a plurality of unit cells, comprising a substrate, a front electrode layer, an absorber layer and a back electrode layer stacked in such a sequence. The thin-film solar cell further includes at least a defect formed at least in the back electrode layer, and the defect has at least an isolation groove of a closed curve formed around the defect.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a thin-film solar cell and, more particularly, to a thin-film solar cell having a defect surrounded by an isolation groove. 
         [0003]    2. Description of Related Art 
         [0004]    Generally, a thin-film solar cell is formed at least of a transparent substrate, a front electrode layer, an absorber layer, and a back electrode layer sequentially stacked up. During the manufacturing process of a thin-film solar cell, the foregoing layers are deposited and laser light cut so as to form a thin-film solar cell with a plurality of unit cells connected in series. While the layers are being laser light cut, any incomplete cut becomes a defect that may short-circuit the finished thin-film solar cell and thus lower the overall power generation efficiency thereof. To solve this problem, Japanese Patent Laid-Open Publication No. H8-037317 provides a method for detecting and removing a short-circuiting defect of a thin-film solar cell, wherein the method comprises determining the location of a defect in a back electrode layer by means of infrared thermal image measurement and then removing the defect with pulse laser light according to the location of the defect. 
         [0005]    Nevertheless, the prior art cited above leaves much room for improvement in terms of defect removal from thin-film solar cells. More specifically, the prior art is directed essentially to the removal of a short-circuiting defect located in the back electrode layer of a thin-film solar cell. In practice, however, the defect of a thin-film solar cell may occur in places other than the back electrode layer, and the defect may cause problems other than a short circuit. As the absorber layer and the front electrode layer are also susceptible to defects of various forms during the manufacturing process of a thin-film solar cell, the above-cited prior art has its limitations in improving defect removal from thin-film solar cells. Therefore, it is a pressing issue for the related industry to provide more effective defect removal from thin-film solar cells than that furnished by the prior art. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    To overcome the aforesaid shortcomings of the prior art, the present invention provides a thin-film solar cell embodying a specific way of defect removal such that a defect of the thin-film solar cell is surrounded by an isolation groove. The thin-film solar cell of the present invention, formed at least of a substrate, a front electrode layer, an absorber layer, and a back electrode layer stacked up sequentially, is characterized in that the thin-film solar cell further has at least one defect formed in the back electrode layer, and that the defect has at least an isolation groove of a closed-curve configuration formed around the defect. 
         [0007]    Hence, a primary objective of the present invention is to provide a thin-film solar cell having a defect surrounded by an isolation groove, wherein the isolation groove is formed by removing a portion of a back electrode layer of the thin-film solar cell with one of ultraviolet laser light, green laser light, and infrared laser light. 
         [0008]    A secondary objective of the present invention is to provide a thin-film solar cell having a defect surrounded by an isolation groove, wherein the isolation groove is formed by further removing a portion of an absorber layer of the thin-film solar cell with one of green laser light and infrared laser light. 
         [0009]    Yet another objective of the present invention is to provide a thin-film solar cell having a defect surrounded by an isolation groove, wherein the isolation groove is formed by further removing a portion of a front electrode layer of the thin-film solar cell with infrared laser light. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The structures and technical means adopted by the present invention to achieve the above and other objectives can be best understood by referring to the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1A  is a schematic top view of a first preferred embodiment of the present invention, showing steps of forming an isolation groove in a thin-film solar cell having a defect; 
           [0012]      FIG. 1B  is a schematic side sectional view of the first preferred embodiment taken along line A-A of  FIG. 1A  so as to show a first structure of the isolation groove; 
           [0013]      FIG. 1C  is another schematic side sectional view of the first preferred embodiment taken along line A-A of  FIG. 1A  so as to show a second structure of the isolation groove; 
           [0014]      FIG. 2A  is a schematic top view of a second preferred embodiment of the present invention, showing steps of forming a first isolation groove and a second isolation groove in a thin-film solar cell having a defect; 
           [0015]      FIG. 2B  is a schematic side sectional view of the second preferred embodiment taken along line B-B of  FIG. 2A  so as to show structures of the first and second isolation grooves; 
           [0016]      FIG. 2C  is another schematic side sectional view of the second preferred embodiment taken along line B-B of  FIG. 2A  so as to show other structures of the first and second isolation grooves; 
           [0017]      FIG. 3A  is a schematic top view of a third preferred embodiment of the present invention, showing steps of forming a first isolation groove, a second isolation groove, and a third isolation groove in a thin-film solar cell having a defect; 
           [0018]      FIG. 3B  is a schematic side sectional view of the third preferred embodiment taken along line C-C of  FIG. 3A  so as to show structures of the first, second, and third isolation grooves; and 
           [0019]      FIG. 3C  is another schematic side sectional view of the third preferred embodiment taken along line C-C of  FIG. 3A  so as to show other structures of the first, second, and third isolation grooves. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention provides a thin-film solar cell, wherein the principle of photoelectric conversion from solar energy is well known to a person of ordinary skill in the art and therefore will not be detailed herein. Besides, it is to be understood that the drawings referred to in the following description are intended to demonstrate features of the present invention only schematically, so the drawings are not necessarily drawn to scale. 
         [0021]    A first preferred embodiment of the present invention is shown in FIG  1 A and  FIG. 1B , which illustrate steps of forming an isolation groove in a thin-film solar cell having a defect. As shown in the drawings, a thin-film solar cell  10  is formed at least of a substrate  11 , a front electrode layer  12 , an absorber layer  13 , and a back electrode layer  14  stacked up sequentially. The thin-film solar cell  10  further has at least one defect  15 . At least one isolation groove  16  having a closed-curve configuration is formed around the defect  15  according to which layer of the thin-film solar cell  10  the defect  15  is in. 
         [0022]      FIG. 1B  is a sectional view taken along line A-A of FIG  1 A and shows a first structure of the isolation groove  16  formed in the thin-film solar cell  10  of the first preferred embodiment. The isolation groove  16  in  FIG. 1B  is formed when the defect  15  is located in the back electrode layer  14 . More specifically, the back electrode layer  14  is partially removed with ultraviolet laser light, green laser light, or infrared laser light along a closed curve centered around the defect  15 . Thus, the isolation groove  16  having a closed-curve configuration is formed in the back electrode layer  14  to isolate the defect  15  of the thin-film solar cell  10 . 
         [0023]    Please refer to  FIG. 1C , which is another sectional view taken along line A-A of  FIG. 1A , for a second structure of the isolation groove  16  formed in the thin-film solar cell  10  of the first preferred embodiment. The isolation groove  16  in  FIG. 1C  is formed when the defect  15  is located in the absorber layer  13 . More specifically, the back electrode layer  14  and the absorber layer  13  are partially removed with green laser light or infrared laser light along a closed curve centered around the defect  15 . Thus, the isolation groove  16  having the second structure that extends from the back electrode layer  14  through the absorber layer  13  is formed to isolate the defect  15  of the thin-film solar cell  10 , thereby increasing overall power generation efficiency of the thin-film solar cell  10 . 
         [0024]    A second preferred embodiment of the present invention is shown in  FIG. 2A  and  FIG. 2B , which illustrate steps of forming isolation grooves in a thin-film solar cell having a defect. As shown in the drawings, a thin-film solar cell  20  is formed at least of a substrate  21 , a front electrode layer  22 , an absorber layer  23 , and a back electrode layer  24  sequentially stacked up. The thin-film solar cell  20  further has at least one defect  25 . A second isolation groove  27  and a first isolation groove  26  are formed successively around the defect  25  according to which layer of the thin-film solar cell  20  the defect  25  is in. The second isolation groove  27  has a closed-curve configuration. 
         [0025]      FIG. 2B  is a sectional view taken along line B-B of  FIG. 2A  and shows structures of the first isolation groove  26  and the second isolation groove  27  formed in the thin-film solar cell  20  of the second preferred embodiment. When the defect  25  is located in the front electrode layer  22 , the back electrode layer  24 , the absorber layer  23 , and the front electrode layer  22  are partially removed with infrared laser light along a closed curve centered around the defect  25 , thereby forming the second isolation groove  27 . Following that, only the back electrode layer  24  is partially removed with ultraviolet laser light, green laser light, or infrared laser light along a path which runs outside and along the second isolation groove  27  and is centered around the defect  25 , thereby forming the first isolation groove  26 . The second isolation groove  27  is adjacent to the first isolation groove  26 . Moreover, the second isolation groove  27  has a groove width smaller than or equal to that of the first isolation groove  26 . Consequently, the defect  25  of the thin-film solar cell  20  is isolated to increase overall power generation efficiency of the thin-film solar cell  20 . 
         [0026]    Please refer to  FIG. 2C , which is another sectional view taken along line B-B of  FIG. 2A , for other structures of the first and second isolation grooves  26 ,  27  formed in the thin-film solar cell  20  of the second preferred embodiment. In this case, formation of the second isolation groove  27  also corresponds to the defect  25  in the front electrode layer  22 . To begin with, the back electrode layer  24 , the absorber layer  23 , and the front electrode layer  22  are partially removed with infrared laser light along a closed curve centered around the defect  25 , thereby forming the second isolation groove  27 . Next, green or infrared laser light output is directed along a path which runs outside and along the second isolation groove  27  and is centered around the defect  25 , so as to partially remove not only the back electrode layer  24  but also the absorber layer  23  as the laser light output further extends from the back electrode layer  24  through the absorber layer  23 , thereby forming the first isolation groove  26 . The second isolation groove  27  is adjacent to the first isolation groove  26 . Moreover, a groove width of the second isolation groove  27  in the absorber layer  23  is smaller than or equal to a groove width of the first isolation groove  26  in the back electrode layer  24 . As a result, the defect  25  of the thin-film solar cell  20  is isolated to increase overall power generation efficiency of the thin-film solar cell  20 . 
         [0027]    A third preferred embodiment of the present invention is shown in  FIG. 3A  and  FIG. 3B , which illustrate steps of forming isolation grooves in a thin-film solar cell having a defect. As shown in the drawings, a thin-film solar cell  30  is formed at least of a substrate  31 , a front electrode layer  32 , an absorber layer  33 , and a back electrode layer  34  sequentially stacked up. The thin-film solar cell  30  further has at least one defect  35 . A first isolation groove  36 , a second isolation groove  37 , and a third isolation groove  38  are formed successively around the defect  35  according to which layer of the thin-film solar cell  30  the defect  35  is in. The second isolation groove  37  has a closed-curve configuration. 
         [0028]      FIG. 3B  is a sectional view taken along line C-C of  FIG. 3A  and shows structures of the first, second and third isolation grooves  36 ,  37 ,  38  formed in the thin-film solar cell  30  of the third preferred embodiment. When the defect  35  is in the front electrode layer  32 , the back electrode layer  34  is partially removed with ultraviolet laser light, green laser light, or infrared laser light along a path centered around the defect  35 , thereby forming the first isolation groove  36 . Next, the back electrode layer  34 , the absorber layer  33 , and the front electrode layer  32  are partially removed with infrared laser light along a closed curve which surrounds the first isolation groove  36  and is centered around the defect  35 , thereby forming the second isolation groove  37  having a closed-curve configuration. Finally, the back electrode layer  34  is partially removed with ultraviolet laser light, green laser light, or infrared laser light along a path centered around the defect  35 , thereby forming the third isolation groove  38 . The third isolation groove  38  is adjacent to the second isolation groove  37 , and the second isolation groove  37  is adjacent to the first isolation groove  36 . Furthermore, the third isolation groove  38  has a groove width smaller than or equal to that of the second isolation groove  37 , and the groove width of the second isolation groove  37  is smaller than or equal to that of the first isolation groove  36 . Consequently, the defect  35  of the thin-film solar cell  30  is isolated to increase overall power generation efficiency of the thin-film solar cell  30 . 
         [0029]    Please refer to  FIG. 3C , which is another sectional view taken along line C-C of  FIG. 3A , for another structure of the first, second and third isolation grooves  36 ,  37 ,  38  formed in the thin-film solar cell  30  of the third preferred embodiment. To begin with, the back electrode layer  34  and the absorber layer  33  are partially removed with green laser light or infrared laser light along a path centered around the defect  35 , thereby forming the first isolation groove  36 . Following that, infrared laser light output is directed along a closed curve which surrounds the first isolation groove  36  and is also centered around the defect  35 , so as to partially remove not only the back electrode layer  34  and the absorber layer  33  but also the the front electrode layer  32  as the infrared laser light output extends the front electrode layer  32  from the back electrode layer  34  through the absorber layer  33 , thereby forming the second isolation groove  37 . Finally, the back electrode layer  34  and the absorber layer  33  are partially removed with green laser light or infrared laser light along a path which runs outside and along the second isolation groove  37  and is centered around the defect  35 , thereby forming the third isolation groove  38 . The third isolation groove  38  is adjacent to the second isolation groove  37 , and the second isolation groove  37  is adjacent to the first isolation groove  36 . Moreover, the third isolation groove  38  has a groove width smaller than or equal to that of the second isolation groove  37 , and the groove width of the second isolation groove  37  is smaller than or equal to that of the first isolation groove  36 . Consequently, the defect  35  of the thin-film solar cell  30  is isolated to increase overall power generation efficiency of the thin-film solar cell  30 . 
         [0030]    In the first, second, and third preferred embodiments of the present invention, the groove width of each isolation groove ranges from 0.001 μm to 100000 μm, and the closed-curve configurations of those isolation grooves having the same can be any one of a rectangle, a triangle, a polygon, a circle, an ellipse, or an island shape. 
         [0031]    The present invention is described herein by reference to the preferred embodiments, and it is understood that the embodiments are not intended to limit the scope of the present invention. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the spirit of the present invention should be encompassed by the appended claims.