Abstract:
A thin film solar cell and a manufacturing method thereof have been disclosed in the present invention. According to the present invention, the thin film solar cell with an isolation groove can prevent generating short paths between electrodes from occurring.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to a thin film solar cell and a manufacturing method thereof. In particular, the solar cell has improved effects of isolation. 
       BACKGROUND OF THE INVENTION 
       [0002]    A solar cell utilizes the conversion of a light energy into an electric energy. The solar cell is formed in a PN-junction, wherein a positive semiconductor (P) makes a junction with a negative semiconductor (N). When a solar cell receives light with the PN-junction structure, holes and electrons are generated in the semiconductor due to the energy of the solar light. The holes are drifted toward the P-type semiconductor, and the electrons are drifted toward the N-type semiconductor in the electric field resulting from the PN-junction area. Consequently, an electric power is produced by the occurrence of electric potential. 
         [0003]    As known in the field, the solar cell can be classified into a wafer type solar cell and a thin film solar cell. The wafer solar cell uses a wafer made of a semiconductor material such as silicon, and the thin film solar cell is made by forming a semiconductor in the form of a thin film on a glass substrate. 
         [0004]    A monolithic thin film solar cell is manufactured by sequential steps. In a conventional manufacturing process of a thin film solar cell, a front electrode layer is deposited onto a substrate first, then the first electrode layer is laser-scribed, which forms numbers of grooves; a semiconductor layer is subsequently deposited onto the front electrode and then laser-scribed, which forms numbers of grooves; a back electrode is then deposited onto the semiconductor, followed by laser-scribing the back electrode layer and the semiconductor layer, and resulted grooves. By laser-scribing the above-mentioned deposited layers, a thin film solar cell comprised of numbers of unit cells serially connected to each other is obtained. 
         [0005]    To prevent problems like short paths and leakage of electrical currents during packaging from occurring, a standard technique of generating an isolation groove can be found in U.S. Pat. No. 6,300,556. Referring to  FIG. 1 , an isolation groove,  13 , is generally produced by laser-scribing or mechanical cuts. In both cases, a short path between electrodes,  2  and  6 , can be generated and hence reduce the performance of solar modules. An isolation groove is used to separate the solar cells and the boundaries of the module. 
         [0006]    Another application is generating see through solar module or resolving hot spot problem, as shown in U.S. Pat. No. 6,858,461. As shown in  FIG. 2 , the cut  140  removes only top two layers, top electrode and semiconductor layers. In practical, cutting through all three layers is used as well. 
         [0007]    As shown above, a conventional standard technique of creating an isolation groove is by laser-scribing the solar cells after the devices are fabricated. However, parts of the back electrode layer may not be completely removed after laser-scribing due to the variations of temperature in the laser beam, which will lead to residue of the back electrode layer still remain on the front electrode layer, consequently resulting in short paths of electrical currents. In other words, such techniques usually generate random short paths between the front and back electrodes, which would become leakage paths in the solar cells and reduce its performance. Practically, one can monitor such instances by measuring Shunt resistance (Rsh). In addition, the short paths could cause hot spot problem. 
         [0008]    In light of the above-mentioned problems, there is a need for a thin film solar cell with an isolation groove which can prevent generating short paths between electrodes from occurring. A thin film solar cell and the manufacturing method thereof have been disclosed in the prevent invention. 
       SUMMARY OF THE INVENTION 
       [0009]    In some embodiments of the present invention, a thin film solar cell comprises a substrate, a front electrode layer, a semiconductor layer, and a back electrode layer. 
         [0010]    In another embodiment of the present invention, a method for manufacturing a thin film solar cell comprises the following steps: 
         [0011]    (1) providing a substrate first; 
         [0012]    (2) providing a front electrode layer above the substrate; 
         [0013]    (3) using a patterning technique to define grooves in the front electrode layer, which divides the front electrode layer into numbers of units, wherein the substrate is exposed at the grooves; 
         [0014]    (4) using the patterning technique to form a wide groove with a desired width in the front electrode layer at an isolation area, or using one of the grooves in the front electrode layer as the wide groove, wherein the substrate is exposed at the wide groove and the width of said wide groove is equal to or greater than the width of the grooves in the front electrode layer; 
         [0015]    (5) providing a semiconductor layer formed above the front electrode layer; 
         [0016]    (6) using a patterning technique to form grooves in the semiconductor layer, which divide the semiconductor layer into numbers of units, wherein the front electrode layer is exposed at the grooves; 
         [0017]    (7) providing a back electrode layer formed above the semiconductor layer; 
         [0018]    (8) using a patterning technique to form grooves in the back electrode layer or in the back electrode layer and the semiconductor layer, which to divide the back electrode layer into numbers of units, wherein the semiconductor layer or the front electrode layer is exposed at the grooves; and 
         [0019]    (9) using the patterning technique at the isolation area above the wide groove to remove layers, which forms an isolation groove extending downward, wherein the substrate is exposed at the isolation groove. 
         [0020]    In another embodiment of the present invention, a method for manufacturing a thin film solar cell is provided as well. The method comprises: 
         [0021]    (1′) providing a substrate; 
         [0022]    (2′) providing a front electrode layer formed above the substrate; 
         [0023]    (3′) using a patterning technique to define grooves in the front electrode layer, which divide the front electrode layer into numbers of units, wherein the substrate is exposed at the grooves; 
         [0024]    (4′) using the patterning technique to form at least two grooves in the front electrode layer at an isolation area, wherein the distance between each of the at least two grooves is predetermined and the substrate is exposed at the grooves, wherein the distance between each of the at least two grooves is preferably in the range of 0 to 1 cm; 
         [0025]    (5′) providing a semiconductor layer formed above the front electrode layer; 
         [0026]    (6′) using a patterning technique to form grooves in the semiconductor layer, which divide the semiconductor layer into numbers of units, wherein the front electrode layer is exposed at the grooves; 
         [0027]    (7′) providing a back electrode layer formed above the semiconductor layer; 
         [0028]    (8′) using a patterning technique to form grooves in the back electrode layer or in the back electrode layer and the semiconductor layer, which divide the semiconductor layer into numbers of units, wherein the semiconductor layer or the front electrode layer is exposed at the grooves; and 
         [0029]    (9′) using the patterning technique at the isolation area above the at least two grooves or the region in between two grooves to remove layers, which forms an isolation groove extending downward, wherein the substrate or the front electrode layer is exposed at the isolation groove. 
         [0030]    In a further embodiment, the invention is to propose a new method for generating isolation grooves in thin film solar cells with no chance of generating short paths between electrodes, which is easy to carry out and will improve the effects of isolation in the thin film solar cells, thereby preventing the problem of short paths from occurring. Therefore, the performance of the thin film solar cell can be improved. Still further, the occurrence of the hot spot problem can be also reduced by the technique of this invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The structure and the 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 and the accompanying diagrams. 
           [0032]      FIG. 1  shows a schematic cross sectional view that shows a thin film solar cell in the prior art. 
           [0033]      FIG. 2  shows a schematic view that shows a thin film solar cell in the prior art. 
           [0034]      FIGS. 3A and 3B  show schematic cross sectional views depicting a process flow of an embodiment of the present invention. 
           [0035]      FIGS. 4A to 4C  show schematic cross sectional views depicting a process flow of another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    A thin film solar cell and a manufacturing method thereof have been disclosed in the present invention, wherein the methods and principles of photoelectric conversion used in solar cells are well known to persons having ordinary skill in the art, and thus will not be further described hereafter. 
         [0037]    For better understanding, the present invention is illustrated below in details by an embodiment with reference to the drawings, which are not intended to limit the scope of the present invention. It will be apparent that any modifications or alterations that can easily be accomplished by those having ordinary skill in the art fall within the scope of the disclosure of the specification. 
         [0038]    As well known in the field, the patterning technique used in the present invention can be, but not limited to, laser-scribing, mechanical means, chemical etching, and photolithography. For example, the chemical etching comprises dry etching, wet etching, and etching paste. 
         [0039]    Referring to  FIG. 3A , a preferred embodiment is disclosed in the present invention, illustrating a method for manufacturing a thin film solar cell. The method comprises: 
         [0040]    (a1) providing a substrate  40 ; 
         [0041]    (a2) providing a front electrode layer  41  formed above the substrate  40 ; 
         [0042]    (a3) laser-scribing the front electrode layer  41  to form a plurality of first grooves  42 , which divides the front electrode layer  41  into numbers of units, wherein the substrate is exposed at the first grooves  42 ; 
         [0043]    (a4) laser-scribing the front electrode layer  41  to form a wide groove  43  with a desired width in the front electrode layer at an isolation area, wherein the wide groove  43  has a width greater than that of the first grooves  42  and the substrate is exposed at the wide groove  43 ; 
         [0044]    (a5) providing a semiconductor layer  44  formed above the front electrode layer  41  and the exposed substrate  40 ; 
         [0045]    (a6) laser-scribing the semiconductor layer  44  to form a plurality of second grooves  45 , which divides the semiconductor layer  44  into numbers of units, wherein the front electrode layer is exposed at the second grooves  45 ; 
         [0046]    (a7) providing a back electrode layer  46  formed above the semiconductor layer  44  and the exposed front electrode layer  41 ; 
         [0047]    (a8) etching the back electrode layer  46  to form a plurality of third grooves  47 , which divides the back electrode layer  46  into numbers of units, wherein the semiconductor layer  44  is exposed at the third grooves  47 ; and 
         [0048]    (a9) laser-scribing the back electrode layer  46  and the semiconductor layer  44  at the wide groove  43  downward, which forms an isolation groove  49  at the isolation area, wherein the substrate  40  is exposed at the isolation groove  49 . 
         [0049]    In another preferred embodiment which is similar to the above-mentioned embodiment, after steps (a1) to (a7) are performed, a plurality of third grooves  47  can be also defined in the back electrode layer  46  and the semiconductor layer  44  by a patterning technique such as laser-scribing according to the demands (not shown in the figures). Then, the following step is to form an isolation groove  49 , which is the same process as the above-mentioned step (a9), and thus will not be further described herein. 
         [0050]    In still another preferred embodiment, the first groove can be used as the wide groove. After steps (a1) to (a3), the first grooves  42  are formed. In this embodiment, the width of the (wide) groove is the same as that of one of the grooves. That is, a first groove  42  at an isolation area  48  is used as the wide groove. Then, after step (a4) is skipped and step (a5) is performed, a semiconductor layer  44  is formed above the front electrode layer  41  and the exposed substrate  40 . After that, performing steps (a6) to (a8) to form the patterned back electrode. Finally, laser-scribing the back electrode layer  46  and the semiconductor layer  44  at the isolation area above the first groove  42  to form the isolation groove  49  Referring to  FIG. 3B , the width of the isolation groove is less than that of the first groove  42 . 
         [0051]    In another preferred embodiment, a method for manufacturing a thin film solar cell is illustrated in  FIG. 4A . The method comprises: 
         [0052]    (b1) providing a substrate  50 ; 
         [0053]    (b2) providing a front electrode layer  51  formed above the substrate  50 ; 
         [0054]    (b3) laser-scribing the front electrode layer  51  to form a plurality of first grooves  52 , which divides the front electrode layer  51  into numbers of units, wherein the substrate  50  is exposed at the first groove  52 ; 
         [0055]    (b4) laser-scribing the front electrode layer  51  at an isolation area  591  to form two grooves  53  and  54  in the front electrode layer  51  at the isolation area, wherein the distance between each of the grooves is predetermined and the substrate is exposed at the grooves  53  and  54 ; 
         [0056]    (b5) providing a semiconductor layer  55  formed above the front electrode layer  51  and the exposed substrate  50 ; 
         [0057]    (b6) laser-scribing the semiconductor layer  55  to form a plurality of second grooves  56 , which divides the semiconductor layer  55  into numbers of units, wherein the front electrode layer  51  is exposed at the second grooves  56 ; 
         [0058]    (b7) providing a back electrode layer  57  formed above the semiconductor layer  55  and the exposed front electrode layer  51 ; 
         [0059]    (b8) etching the back electrode layer  57  to form a plurality of third grooves  58 , which divides the back electrode layer  57  into numbers of units, wherein the semiconductor layer  55  is exposed at the third grooves  58 ; and 
         [0060]    (b9) laser-scribing the layers within the isolation area  591 , which forms an isolation groove  59 , wherein the substrate  50  is exposed at the isolation groove  59 . 
         [0061]    Specifically, referring to  FIG. 4A , the laser-scribing is performed at the isolation area  591  of the back layer  57 , the semiconductor layer  55  and peripheral portion of the front electrode layer  51  to form the isolation groove  59 . Alternatively, referring to  FIG. 4B , the laser-scribing could be also performed at the isolation area  591  of the back layer  57 , the semiconductor layer  55  and central portion of the front electrode layer  51  to form the isolation groove  59 . Alternatively, referring to  FIG. 4C , the laser-scribing is performed at within the isolation area  591  of the back layer  57  and the semiconductor layer  55  to form the isolation groove  59 . In other words, the laser-scribing can be performed in two layers or three layers at the isolation area  591  according to the demands. In this embodiment, a better position tolerance on scribing the back electrode layer to form the isolation groove  59  is obtained due to the isolation groove  59  could be defined within the isolation area  591 . 
         [0062]    In another preferred embodiment which is similar to the above-mentioned embodiment, after steps (b1) to (b7) are performed, a plurality of third grooves  58  can be also defined in the back electrode layer  57  and the semiconductor layer  55  by a patterning technique such as laser-scribing according to the demands (not shown in the figures). Then, the following step is to form an isolation groove  59 , which is the same process as the above-mentioned step (b9), and thus will not be further described herein. 
         [0063]    The front electrode layer includes grooves which divide the front electrode into units. The semiconductor layer is formed above the substrate with grooves which divide the semiconductor layer into units after the front electrode is formed. The back electrode layer is then formed above the semiconductor layer with grooves which divide the back electrode layer into units. 
         [0064]    After the solar cell is fabricated, an isolation groove is created at the isolation area according to the demands. For example, the isolation groove could be defined at the peripheral part of the solar cell and is extending downward so as the substrate or the front electrode of the solar cell is exposed at the isolation groove. 
         [0065]    Furthermore, the use of the isolation groove comprises, but is not limited to, doing edge deletion, hot spot solution, or see through solar panels. For example, when the isolation groove is used for edge deletion, the isolation groove is generally defined right at the periphery of the panels by laser-scribing or mechanical means. 
         [0066]    When the grooves are formed in the semiconductor layer, an offset between each of the grooves in the front electrode layer and each of the grooves in the semiconductor layer exists. Similarly, another offset exists between each of the grooves in the semiconductor layer and each of the grooves in the back electrode layer. The offsets in the solar cell are in the range of 0 to 500 μm, preferably in the range of 5 to 500 μm. 
         [0067]    Although the present invention has been described with reference to the illustrative embodiment, it should be understood that any modifications or alterations that can easily be accomplished by persons having ordinary skill in the art will fall within the scope of the disclosure of the specification, drawings, and the appended claims.