Patent Publication Number: US-2020303572-A1

Title: Thin film solar cell

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Patent Application No. 201810102076.3, filed on Feb. 1, 2018, titled “THIN FILM SOLARY CELL MODULE”, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a solar cell technical field, and in particular, to a thin film solar cell. 
     BACKGROUND 
     The solar thin film cell is also called ‘solar chip’ or ‘photovoltaic cell’, which is a kind of optoelectronic semiconductor component using sunlight to generate electricity directly. 
     One step in the preparation process of the thin film solar cell is to use at least 3 laser/mechanical scribing processes (according to the chronological order of the scribing, it is named that P1 scribing, P2 scribing, and P3 scribing), to divide the whole thin film solar cell into a plurality of cell units, and series connection or parallel connection is realized among the plurality of cell units. 
     SUMMARY 
     Several embodiments of the present disclosure provides a thin film solar cell, comprising a substrate and a plurality of cell units disposed on the substrate, each cell unit among the plurality of cell units comprises a back electrode layer, a light absorbing layer, a buffer layer, and an upper electrode layer which are sequentially disposed, wherein, a first groove throughout the back electrode layer is disposed between the back electrode layers of any two adjacent cell units among the plurality of cell units, the first groove is filled with an insulating portion, so as to insulate the back electrode layers of the two adjacent cell units, a second groove throughout the light absorbing layer and the buffer layer is disposed in each cell unit among the plurality of cell units, the upper electrode layer of any one cell unit of the two adjacent cell units covers the buffer layer of this cell unit and extends to the second groove of this cell unit to contact the back electrode layer of the other cell unit in the two adjacent cell units, and then which connects the two adjacent cell units in series, a third groove is disposed between the two adjacent cell units, the third groove insulates the upper electrode layers of the two adjacent cell units. 
     Several embodiments of the present disclosure further provides a method for preparing the thin film solar cell, comprising: forming a back electrode layer on the substrate; forming a first groove on the back electrode layer by performing the first scribing process; forming an insulating portion located in the first groove; sequentially forming a light absorbing layer and a buffer layer on the surface of the back electrode layer which is formed with the insulating portion, and performing a second scribing process to the light absorbing layer and the buffer layer to form a second groove throughout the light absorbing layer and the buffer layer; forming an upper electrode layer on the surface of the buffer layer, and extending the upper electrode layer to the second groove, so that the upper electrode layer of any one cell unit of the two adjacent cell units contacts the back electrode layer of the other adjacent cell unit in the two adjacent cell units; performing a third scribing process to the upper electrode layer, the buffer layer, and the light absorbing layer to form a third groove throughout the upper electrode layer, the buffer layer, and the light absorbing layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings here are used to provide further understanding of the present disclosure and constitute a part of the present disclosure. The schematic embodiments of the present disclosure and the illustrations thereof serve to explain the present disclosure ;  but do not constitute an improper limitation to the disclosure. In the accompanying drawings, 
         FIG. 1  is the schematic diagram of the structure of the thin film solar cell according to the present disclosure; 
         FIG. 2  is the schematic diagram of the preparation process of the thin film solar cell according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solutions in the embodiments of the present disclosure will be described clearly and completely. Obviously, the described embodiments are merely some but not all of embodiments of the present disclosure. All other embodiments made on the basis of the embodiments of the present disclosure by a person of ordinary skill in the art without paying any creative effort shall be included in the protection scope of the present disclosure. 
     Although the P1, P2, and P3 scribing processes may form a plurality of series/parallel-connected cell units, at the same time, an area (spacer region between the positions of P1˜P3 scribing lines and the adjacent scribing lines) incapable of photoelectric conversion may be generated in the thin film solar cell, i.e. so-called ‘dead zone’ in the thin film solar cell. 
     P1, P2, and P3 scribing processes are realized by laser or mechanical scribing, limited by the prior scribing process technological level and cost control factors, the width and accuracy of the P1˜P3 scribing lines are difficult to be improved, causing the area of dead zone cannot be effectively reduced, ultimately affecting the light conversion efficiency of the thin film solar cell. 
     Referring to  FIG. 1 , several embodiments of the present disclosure provides a thin film solar cell. The thin film solar cell comprises a substrate  10  and a plurality of cell units disposed on the substrate  10 . Each cell unit among the plurality of cell units comprises a back electrode layer  20 , a light absorbing layer  30 , a buffer layer  40 , and an upper electrode layer  50  which are sequentially disposed. A first groove  60  throughout the back electrode layer  20  is disposed between the back electrode layers  20  of the two adjacent cell units. The first groove  60  is filled with an insulating portion  70 , so as to insulate the back electrode layers  20  of the two adjacent cell units. A second groove  80  throughout the light absorbing layer  30  and the buffer layer  40  is disposed in each cell unit. The upper electrode layer  50  covers the buffer layer  40  and extends to the second groove  80  to contact the back electrode layer  20  of the other cell unit, and then connecting the other adjacent cell unit in series. A third groove  90  is disposed between the two adjacent cell units; the third groove  90  insulates the upper electrode layers  50  of the two adjacent cell units. 
     The thin film solar cell has the following advantage: since the insulating portion is set in the first groove, that is the back electrode layers among the plurality of cell units are disposed at interval via the insulating portion, so that the second groove may be formed on partial surface of the insulating portion, the insulating portion may be partly exposed by the second groove, the space between the position of the second groove and the position of the groove is reduced, and thus, the area of the dead zone is greatly reduced, thereby the conversion efficiency of the thin film solar cell is greatly improved. 
     In several embodiments of the present disclosure, the insulating portion is disposed on the position of the first scribing line (i.e. P1 scribing) of the thin film solar cell, i.e. back electrode layers among the plurality of cell units are disposed at interval via the insulating portion, thereby the second scribing (i.e. P2 scribing) can be performed on partial surface of the insulating portion, so as to reduce the area of the dead zone. 
     In the corresponding preparation method of the thin film solar cell, the first groove may be formed by the first scribing process, and the insulating portion is formed in the first groove by a mask, so that the second scribing may be performed on partial surface of the insulating portion. The interval between the position of the first scribing line and the position of the second scribing line is reduced, and thus, the area of the dead zone is greatly reduced. The method has the advantages of simple process, high efficiency and be easy to control. 
     As shown in  FIG. 1 , the following describes the structure of the thin film solar cell by taking the adjacent first cell unit  100  and second cell unit  200  in the thin film solar cell as an example. 
     The first cell unit  100  is adjacent to and has the same structure with the second cell unit  200 . That is, the first cell unit  100  and the second cell unit  200  are actually repeating cell units with the same structure, but are specifically named differently to better explain the relationship between the elements in the two adjacent battery units. The first cell unit  100  comprises a first back electrode layer  21 , a first light absorbing layer  31 , a first buffer layer  41 , and a first upper electrode layer  51  which are sequentially disposed. The second cell unit  200  comprises a second back electrode layer  22 , a second light absorbing layer  32 , a second buffer layer  42 , and a second upper electrode layer  52  which are sequentially disposed. The first cell unit  100  shares the substrate  10  with the second cell unit  200 . The first back electrode layer  21  is separated from the second back electrode layer  22  by an insulating portion. Referring to  FIG. 2 , the first light absorbing layer  31  and the first buffer layer  41  have a second groove  80  throughout the first light absorbing layer  31  and the first buffer layer  41  along the thickness direction of the first light absorbing layer  31  and the first buffer layer  41 . The first upper electrode layer  51  covers the first buffer layer  41  and extends to the second groove  80  to cover part of the second back electrode layer  22 , so as to electrically connect with the second back electrode layer  22 , i.e. the bottom of the second groove  80  exposes part of the second back electrode layer  22 , the first upper electrode layer  51  extending to the bottom of this second groove  80  covers and contacts this part of the second back electrode layer  22 , the first cell unit  100  is electrically connected with the second cell unit  200  to realize series connection. 
     In several embodiments of the present disclosure, the portion of the first upper electrode layer  51  extending to the second groove  80  covers the insulating portion  70 , in several other embodiments of the present disclosure, the portion of the first upper electrode layer  51  extending to the second groove  80  does not cover the insulating portion  70 . That is, in several embodiments of the disclosure, the second groove  80  may overlap with the first groove  60  formed by the first scribing (P1 scribing), or may not. 
     In several embodiments of the present disclosure, the bottom of the second groove  80  is located at the border of the insulating portion  70  and the back electrode layer of the other adjacent cell unit, the upper electrode layer located in the second groove  80  covers part of the insulating portion and part of the back electrode layer of the other adjacent cell unit. Referring to  FIG. 1 , in another words, the first upper electrode layer  51  covers the first buffer layer  41  and extends to the second groove  80  to cover part of the second back electrode layer  22  and part of the insulating portion  70 , At this point, the width of the overlapping area between the portion of the first upper electrode layer  51  extending to the second groove  80  and the insulating portion  70  is represented as d 1 . The width of the insulating portion is represented as m. m and d 1  satisfy the following conditions: m&gt;d 1 &gt;0. Wherein, the reason to define m&gt;d 1  is to avoid a short circuit caused by the contact of the portion of the first upper electrode layer  51  extending to the second groove  80  with the first back electrode layer  21 . In some embodiments, m and d 1  preferably satisfy the following conditions: m-d 1 ≥30 μm, so as to avoid this kind of short circuit. 
     The insulating portion  70  is used to separate the first back electrode layer  21  from the second back electrode layer  22  to insulate them from each other, so as to realize the relative independence between the first cell unit  100  and the second cell unit  200 . In several embodiments of the present disclosure, the width m of the insulating portion  70  satisfies the following conditions: 30 μm≤m≤60 μm, so as to better achieve the insulation effect. In several embodiments of the present disclosure, the width m of the insulating portion  70  satisfies the following conditions: the width m is larger than or equal to approximately 30 μm, smaller than or equal to approximately 60 μm. 
     In several embodiments of the present disclosure, the first groove is filled with the insulating portion  70  by mask deposition. 
     In several embodiments of the present disclosure, the material of the insulating portion  70  comprises at least one of Si 3 N 4 , AlN, SiO 2 , and Al 2 O 3 . For example, the material of the insulating portion  70  is Si 3 N 4 . In several other embodiments of the present disclosure, the material of the insulating portion  70  comprises at least several of Si 3 N 4 , AlN, SiO 2 , and Al 2 O 3 . For example, the material of the insulating portion  70  is the composite film layer of Si 3 N 4  and SiO 2 . 
     The width of the second groove  80  can be any size. In several embodiments of the present disclosure, the width of the second groove  80  is 50  82  m˜80  82  m, which can better electrically connect with the electrode and reduce the size of the dead zone. In several embodiments of the present disclosure, the width of the second groove  80  is approximately 50  82  m˜80  82  m. 
     In several embodiments of the present disclosure, the first cell unit  100  is separated from the second cell unit  200  by the third groove  90 . The third groove  90  separates the first upper electrode layer  51  from the second upper electrode layer  52 , separates the first buffer layer  41  from the second buffer layer  42 , and separates the first light absorbing layer  31  from the second light absorbing layer  32 . 
     In several embodiments of the present disclosure, the width of the third groove  90  is 50  82  m˜80  82  m or, approximately 50  82  m˜80  82  m. 
     The third groove  90  cooperates with the insulating portion  70  to achieve the “relatively independent” between the first cell unit  100  and the second cell unit  200 . The reason why it is “relatively independent” is that the first upper electrode layer  51  in the second groove  80  can realize the series connection between the first cell unit  100  and the second cell unit  200 . 
     The material of the substrate  10  is not limited, which may be glass, stainless steel or flexible materials. The thickness of the substrate  10  is also not limited. The substrate  10  plays a role of bearing the solar cell. 
     The material of the back electrode layer  20  may be metal Mo, Ti, Cr, Cu or a transparent conductive layer. The transparent conductive layer comprises one or more of aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (AZO), and indium-doped tin oxide (ITO). The thickness back electrode layer  20  is not limited, In several embodiments of the present disclosure, the thickness of the back electrode layer  20  is 200 nm˜80 nm. In several embodiments of the present disclosure, the thickness of the insulating portion  70  is the same as the thickness of the back electrode layer  20 . In several embodiments of the present disclosure, the thickness of the insulating portion  70  may also be greater than the thickness of the back electrode layer  20 , in order to effectively prevent forming a short circuit. 
     The material of the light absorb layer  30  is one of copper indium gallium selenide, copper indium selenide, and copper indium gallium sulfide. The thickness of the light absorbing layer  30  is not limited. In several embodiments of the present disclosure, the thickness of the light absorbing layer  30  is 0.5  82  m˜3  82  m. 
     The material of the buffer layer  40  is one of zinc sulfide, cadmium sulfide, and indium sulfide. The thickness of the buffer layer  40  is not limited. In several embodiments of the present disclosure, the thickness of the buffer layer  40  is 30 nm˜100 nm. 
     The material of the upper electrode layer  50  is one of transparent conductive layer AZO, BZO and ITO. The thickness of the upper electrode layer  50  is not limited. In several embodiments of the present disclosure, the thickness of the upper electrode layer  50  is 100 nm˜1  82  m. 
     In several embodiments of the present disclosure, other functional layers are added between any two of the electrode layer, the light absorbing layer, the buffer layer, and the upper electrode layer, the examples of the functional layers are zinc oxide layers, and zinc magnesium oxide layers, etc., so that the layers are intimately coupled with each other, and light absorption and conversion are facilitated. 
     Referring to  FIG. 2 , the embodiment of the present disclosure further provides a method for preparing the thin film solar cell. The method comprises the following steps: 
     a) Providing a substrate  10 , and forming a back electrode layer  20  on the substrate  10 , and forming a plurality of first grooves  60  throughout the back electrode layer  20  on the back electrode layer  20  by the first scribing to the back electrode layer  20 ; 
     b) Forming an insulating portion  70  in the first groove  60 ; and 
     c) Sequentially forming a light absorbing layer  30  and a buffer layer  40  on the surface of the back electrode layer  20  which is formed with the insulating portion  70 , and the light absorbing layer  30  and buffer layer  40  are second scribed to form a second groove throughout the light absorbing layer  30  and buffer layer  40 ; and 
     d) Forming an upper electrode layer  50  on the surface of the buffer layer  40 , so that the upper electrode layer  50  extends to the second groove  80 , and the third scribing is performed to the upper electrode layer  50 , the buffer layer  40 , and the light absorbing layer  30  to form a third groove  90  throughout the upper electrode layer  50 , the buffer layer  40 , and the light absorbing layer  30 , and then a plurality of series-connected cell units are obtained. 
     In the step a), the method of forming the back electrode layer  20  may be chemical vapor deposition method, magnetron sputtering method, and atomic layer deposition method, etc. After the first scribing, the back electrode layer  20  may form a plurality of “sub-back electrode layers” which are similar to the first back electrode layer  21  and the second back electrode layer  22  and are separated apart from each other. The “sub-back electrode layer” is the first back electrode layer  21  and the second back electrode layer  22  as shown in  FIG. 1 . The second scribing and the third scribing in step c) and d) is to scribe to the light absorbing layer  30 , buffer layer  40  and the upper electrode layer  50  to form relatively independent and series-connected cell units. The first cell unit  100  and the second cell unit  200  showed in  FIG. 1  are the specially named for better illustrating the relationship between the elements in the two adjacent cell units. In practice, the structures of the first cell unit  100  and the second cell unit  200 , and the corresponding elements thereof are the same. 
     Hereinafter, the description of the light absorbing layer  30  can refer to the above description of the first light absorbing layer  31  and the second light absorbing layer  32 . The description of the buffer layer  40  can refer to the above description of the first buffer layer  41  and the second buffer layer  42 . The description of the upper electrode layer  50  can refer to the above description of the first upper electrode layer  51  and the second upper electrode layer  52 . It will not be described here. 
     In step b), a mask (not shown in figures) is provided, and an insulating portion  70  is formed in the first groove  60  via the mask. The method of forming the insulating portion  70  may be any one of the magnetron sputtering method, the spin coating method, the spray coating method or the chemical vapor deposition method. Wherein, the process of the spin coating method and the spray coating method is: a mixture is obtained by mixing insulating material and solvent such as alcohol, water, etc., then the mixture is spin-coated or spray-coated, the insulating portion  70  is obtained after drying. In several embodiments of the present disclosure, the insulating portion  70  is formed by magnetron sputtering method. 
     In step c), the second groove  80  is formed by the second scribing to the light absorbing layer  30  and the buffer layer  40 . The second groove  80  formed by the second scribing may overlap with part of the first groove  60  formed by the first scribing; or may separate from the first groove  60 , i.e. they are not overlapped. In several embodiments of the present disclosure, the second groove  80  overlaps with part of the first groove  60 , i.e. partial surface of the insulating portion  70  is exposed by the second groove  80 . 
     The width of the insulating portion  70  is represented as m. The width of the partly exposed region of the insulating portion  70  by the second groove  80  is represented as d 1 , in several embodiments of the present disclosure, the width m of the insulating portion  70  is larger than dl. Illustratively, m-d 1 ≥30  82  m. 
     In step a), step c) and step d), the first scribing, the second scribing, and the third scribing can be realized by mechanical scribing or laser scribing. In several embodiments of the present disclosure, the method of the first scribing is laser scribing; the second scribing and the third scribing is mechanical scribing. The widths of the opening of the first groove  60 , the second groove  80  and the third groove  90  are not limited. In several embodiments of the present disclosure, the width of the second groove  80  and the width of the third groove  90  may be 60  82  m˜80  82  m. Illustratively, the interval between the second groove  80  and the third groove  90  is greater than or equal to 30  82  m. 
     The thin film solar cell and the preparation method thereof have the following advantages; 
     Since the insulating portion  70  is disposed in the first groove  60  formed by the first scribing, that is, the back electrode layers among the plurality of cell units are disposed at interval by the insulating portion, and thus the second scribing can be performed on partial surface of the insulating portion  70 . The second scribing forms the second groove  80 , the insulating portion can be partly exposed by the second groove  80 , the interval between the position of the second scribing and the position of the first scribing is reduced, thereby, the area of the dead zone is greatly reduced, so that the conversion efficiency of the thin film solar cell is greatly improved. 
     In this preparation method, the insulating portion  70  is formed in the first groove  60  by the mask, thus the second scribing may be performed on partial surface of the insulating portion  70 , The method has the advantages of simple process, high efficiency and be easy to control. 
     Hereinafter, the thin film solar cell and the preparation method thereof will be further described by the following embodiments. 
     Embodiment 1 
     The present embodiment 1 provides a thin film solar cell. The preparation method of the thin film solar cell follows as below: 
     a) Providing a substrate, and forming a back electrode layer on the substrate by magnetron sputtering method. A first scribing is performed on the back electrode layer, and a plurality of first grooves throughout the back electrode layer are formed on the back electrode layer. 
     In several embodiments, the material of the substrate is glass, the back electrode layer is metal Mo layer, parameters in magnetron sputtering method are: argon is used as an air source, metal Mo is used as a target material, the degree of vacuum is 0.1 Pa to 0.7 Pa; the first scribing is laser scribing, the width of the first groove is approximately 60  82  m. 
     b) Providing a mask, an insulating portion made of Si 3 N 4  is formed in the first groove by magnetron sputtering method. 
     c) Sequentially forming a light absorbing layer and a buffer layer on the surface of the back electrode layer which is formed with the insulating portion, and the light absorbing layer and the buffer layer are secondly scribed to form a second groove throughout the light absorbing layer and the buffer layer, wherein the second scribing is mechanical scribing, the width of the second groove is approximately 50  82  m. The width d 1  of the area of the insulating portion partly exposed by the second groove is approximately 30  82  m. The light absorbing layer is copper indium gallium selenide with a thickness of approximately 3  82  m. The buffer layer is cadmium sulfide with a thickness of approximately 80 nm. 
     d) Forming an upper electrode layer on the surface of the buffer layer, so that the upper electrode layer extends to the second groove, and the third scribing is performed to the upper electrode layer, the buffer layer, and the light absorbing layer to form a third groove throughout the upper electrode layer, the buffer layer, and the light absorbing layer, and then a plurality of series-connected cell units are obtained. Wherein, the third scribing is mechanical scribing. The interval between the third groove and the second groove (i.e, referring to  FIG. 1 , the interval between the right edge of the second groove  80  and the left edge of the third groove  90 ) is 40  82  m, the upper electrode layer is an AZO transparent conductive film having a thickness of about 800 nm, and the third groove has a width of approximately 60  82  m. 
     The width from the first groove to the third groove in the obtained thin film solar cell (i.e. referring to  FIG. 1 , the width from the left edge of the first groove to the right edge of the third groove, the same applies below) is about 180  82  m. 
     Embodiment 2 
     The present embodiment 2 provides a thin film solar cell. The preparation method of the thin film solar cell follows as below: 
     a) Providing a substrate, and forming a back electrode layer on the substrate by magnetron sputtering method. A first scribing is performed on the back electrode layer, and a plurality of first grooves throughout the back electrode layer are formed on the back electrode layer. 
     Wherein, the material of the substrate is glass, the back electrode layer is metal Mo layer, parameters in magnetron sputtering method are: argon is used as an air source, metal Mo is used as a target material, the degree of vacuum is 0.1 Pa to 0.7 Pa. The first scribing is laser scribing, the width of the first groove is approximately 50  82  m. 
     b) Providing a mask, an insulating portion made of Si 3 N 4  is formed in the first groove by magnetron sputtering method. 
     c) Sequentially forming a light absorbing layer and a buffer layer on the surface of the back electrode layer which is formed with the insulating portion, and the light absorbing layer and the buffer layer are secondly scribed to form a second groove throughout the light absorbing layer and the buffer layer. Wherein the second scribing is mechanical scribing, the width of the second groove is approximately 70  82  m. The width dl of the area of the insulating portion partly exposed by the second groove is approximately 15  82  m. The light absorbing layer is copper indium gallium selenide with a thickness of approximately 3  82  m. The buffer layer is cadmium sulfide with a thickness of approximately 80 nm. 
     d) Forming an upper electrode layer on the surface of the buffer layer, so that the upper electrode layer extends to the second groove, and the third scribing is performed to the upper electrode layer, the buffer layer, and the light absorbing layer to form a third groove throughout the upper electrode layer, the buffer layer, and the light absorbing layer, and then a plurality of series-connected cell units are obtained. Wherein, the third scribing is mechanical scribing. The interval between the third groove and the second groove is 40  82  m. The upper electrode layer is an AZO transparent conductive film having a thickness of about 30  82  m. The third groove has a width of approximately 70 pm. 
     The method of preparing the thin film solar cell in the embodiment 2 is substantially the same as that in the embodiment 1, the difference is the width d 1  of the area of the insulating portion partly exposed by the second groove; and the widths of the first groove, the second groove and the third groove. 
     The width from the first groove to the third groove in the obtained thin film solar cell is approximately 215  82  m. 
     Embodiment 3 
     The present embodiment 3 provides a thin film solar cell. The preparation method of the thin film solar cell follows as below: 
     a) Providing a substrate, and forming a back electrode layer on the substrate by magnetron sputtering method. A first scribing is performed on the back electrode layer, and a plurality of first grooves throughout the back electrode layer are formed on the back electrode layer. 
     Wherein, the material of the substrate is glass, the back electrode layer is metal Mo layer, parameters in magnetron sputtering method are: argon is used as an air source, metal Mo is used as a target material, the degree of vacuum is 0.1 Pa to 0.7 Pa. The first scribing is laser scribing, the width of the first groove is approximately 40  82  m. 
     b) Providing a mask, an insulating portion made of Si 3 N 4  is formed in the first groove by magnetron sputtering method. 
     c) Sequentially forming a light absorbing layer and a buffer layer on the surface of the back electrode layer which is formed with the insulating portion, and the light absorbing layer and the buffer layer are secondly scribed to form a second groove throughout the light absorbing layer and the buffer layer. Wherein, the second scribing is mechanical scribing. The width of the second groove is approximately 80  82  m. The width d 1  of the area of the insulating portion partly exposed by the second groove is approximately 5  82  m. The light absorbing layer is copper indium gallium selenide with a thickness of approximately 3  82  m. The buffer layer is cadmium sulfide with a thickness of approximately 80 nm. 
     d) Forming an upper electrode layer on the surface of the buffer layer, so that the upper electrode layer extends to the second groove, and the third scribing is performed to the upper electrode layer, the buffer layer, and the light absorbing layer to form a third groove throughout the upper electrode layer, the buffer layer, and the light absorbing layer, and then a plurality of series-connected cell units are obtained. Wherein, the third scribing is mechanical scribing. The interval between the third groove and the second groove is 40  82  m. The upper electrode layer is an AZO transparent conductive film having a thickness of about 30  82  m. The third groove has a width of approximately 80 μm, 
     The method of preparing the thin film solar cell in the embodiment 3 is substantially the same as that in the embodiment 1, the difference is the width d 1  of the area of the insulating portion partly exposed by the second groove; and the widths of the first groove, the second groove and the third groove. 
     The width from the first groove to the third groove in the obtained thin film solar cell is approximately 235  82  m. 
     Embodiment 4 
     The present embodiment 4 provides a thin film solar cell. The preparation method of the thin film solar cell follows as below: 
     a) Providing a substrate, and forming a back electrode layer on the substrate by magnetron sputtering method. A first scribing is performed on the back electrode layer, and a plurality of first grooves throughout the back electrode layer are formed on the back electrode layer. 
     Wherein, the material of the substrate is glass, the back electrode layer is metal Mo layer, parameters in magnetron sputtering method are: argon is used as an air source, metal Mo is used as a target material, the degree of vacuum is 0.1 Pa to 0.7 Pa. The first scribing is laser scribing, the width of the first groove is approximately 40  82  m. 
     b) Providing a mask, an insulating portion made of Si 3 N 4  is formed in the first groove by magnetron sputtering method. 
     c) Sequentially forming a light absorbing layer and a buffer layer on the surface of the back electrode layer which is formed with the insulating portion, and the light absorbing layer and the buffer layer are secondly scribed to form a second groove throughout the light absorbing layer and the buffer layer. Wherein, the second scribing is mechanical scribing. The width of the second groove is approximately 60  82  m. The insulating portion is not exposed by the second groove (that is, the width d 1  of the area of the insulating portion partly exposed by the second groove is 0). The interval between the second groove and the first groove is 10  82  m. The light absorbing layer is copper indium gallium selenide with a thickness of approximately 3  82  m, and the buffer layer is cadmium sulfide with a thickness of approximately 80 nm. 
     d) Forming an upper electrode layer on the surface of the buffer layer, so that the upper electrode layer extends to the second groove, and the third scribing is performed to the upper electrode layer, the buffer layer, and the light absorbing layer to form a third groove throughout the upper electrode layer, the buffer layer, and the light absorbing layer, and then a plurality of series-connected cell units are obtained, wherein the third scribing is mechanical scribing, the interval between the third groove and the second groove is 40  82  m, the upper electrode layer is an AZO transparent conductive film having a thickness of about 30  82  m, and the third groove has a width of about 60  82  m. 
     The method of preparing the thin film solar cell in the embodiment 4 is substantially the same as that in the embodiment 1, the different is, the position of the first scribing is separated from the position of the second scribing, i.e. after the second scribing in step c), the insulating portion is not exposed by the second groove; and the width of the first groove. 
     The width from the first groove to the third groove in the obtained thin film solar cell is approximately 210  82  m. 
     For better illustrating the excellent performance of the thin film solar cell of the present disclosure, a comparative embodiment is further provided. 
     Comparative Embodiment 
     The present comparative embodiment provides a thin film solar cell module. The preparation method of the thin film solar cell module follows as below: 
     a) Providing a substrate, and forming a back electrode layer on the substrate by magnetron sputtering method. A first scribing is performed on the back electrode layer, and a plurality of first grooves throughout the back electrode layer are formed on the back electrode layer. 
     Wherein, the material of the substrate is glass, the back electrode layer is metal Mo layer, parameters in magnetron sputtering method are: argon is used as an air source, metal Mo as a target material, the degree of vacuum is 0.1 Pa to 0.7 Pa. The first scribing is laser scribing. The width of the first groove is approximately 60  82  m. 
     b) Sequentially forming a light absorbing layer and a buffer layer on the surface of the back electrode layer which is formed with the first groove, and the light absorbing layer and the buffer layer are secondly scribed to form a second groove throughout the light absorbing layer and the buffer layer. Wherein the second scribing is mechanical scribing, the width of the second groove is approximately 60  82  m. The interval between the second groove and the first groove is 40  82  m. The light absorbing layer is copper indium gallium selenide with a thickness of approximately 3  82  m, and the buffer layer is cadmium sulfide with a thickness of approximately 80 nm, 
     c) Forming an upper electrode layer on the surface of the buffer layer, so that the upper electrode layer extends to the second groove, and the third scribing is performed to the upper electrode layer, the buffer layer, and the light absorbing layer to form a third groove throughout the upper electrode layer, the buffer layer, and the light absorbing layer, and then a plurality of series-connected units are obtained. Wherein, the third scribing is mechanical scribing. The upper electrode layer is an AZO transparent conductive film having a thickness of approximately 800 nm, and the third groove has a width of approximately 60  82  m. The interval between the third groove and the second groove is 40  82  m. 
     The method of preparing the thin film solar cell in present comparative embodiment is substantially the same as that in the embodiment 4, the different is, there is no step of forming an insulating portion in the first groove, but to directly form a light absorbing layer on the back electrode layer, i.e. the first groove is filled with a light absorbing layer. 
     The width (which represent the width of the dead zone) from the first groove to the third groove in the obtained thin film solar cell is approximately 260  82  m. It can be seen that compared with the embodiment 1, the area of the dead zone in the comparative embodiment is larger. It can be seen from the above embodiment 1 to embodiment 4, the area of the dead zone of the thin film solar cell may greatly reduced, thus, during the application, the photoelectric conversion efficiency of the thin film solar cell may be greatly improved. 
     The width of the three grooves described above may be adjusted according to the implementation process, which is not limited by the above size, and various technical features of the above described embodiments can be combined randomly, in order to describe concisely, all the possible combinations of each technical features in above embodiments are not described, however, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in present description. 
     The above embodiments are merely illustrative several modes of execution of the present disclosure, the description is more specific and detailed, but it should not be understood as limiting the scope of the present disclosure. It should be noted that, for the person skilled in the art, several variations and improvements may be made without departing from the concept of the present disclosure, and these are all within the protection scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the appended claims.