Patent Publication Number: US-2020303569-A1

Title: Preparation method of thin film solar battery

Description:
This application claims priority to Chinese Patent Application No. 201810102469.4, filed with the Chinese patent office on Feb. 1, 2018, titled “PREPARATION METHOD OF THIN FILM SOLAR BATTERY COMPONENT”, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a technical field of solar battery, more particularly, to a preparation method of a thin film solar battery. 
     BACKGROUND 
     Thin film solar battery, also called “solar chip” or “photocell”, is an optoelectronic semiconductor component that generates electricity directly by using sunlight. 
     Some of the steps in preparation process of a thin film solar battery are; dividing a whole piece of thin film solar battery into a plurality of battery cells by using a laser/mechanical etching process (named P1 etching, P2 etching, and P3 etching respectively in a etching sequence) at least 3 times, and enabling serial or parallel connections between the plurality of battery cells. This process design can ensure the thin film solar battery to realize output at suitable voltage and current, so as to implement practical application of the thin film solar battery. 
     SUMMARY 
     Embodiments of the present disclosure provide a preparation method of a thin film solar battery, including the following steps: 
     a) providing a substrate and forming a back electrode layer thereon, and performing a first etching of the back electrode layer to form a plurality of first grooves on the back electrode layer, the plurality of first grooves all passing through the back electrode layer; 
     b) forming an insulator in each of the plurality of first grooves, thereby forming a plurality of insulators; 
     c) forming a light absorption layer and a buffer layer sequentially on a surface of the back electrode layer formed with the plurality of insulators, and performing a second etching of the light absorption layer and the buffer layer to form a plurality of second grooves, the plurality of second grooves all passing through the light absorption layer and the buffer layer; and 
     d) forming an upper electrode layer on a surface of the buffer layer, the upper electrode layer extending to the plurality of second grooves, and performing a third etching of the upper electrode layer, the buffer layer, and the light absorption layer to form a plurality of third grooves passing through the upper electrode layer, the buffer layer, and the light absorption layer, so as to obtain a plurality of serially connected battery cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are used to provide further understanding of the disclosure and constitute a part of the present disclosure. The following exemplary embodiments together with the explanation thereof serve to explain the present disclosure, but do not constitute an improper limitation to the disclosure. In the accompanying drawings: 
         FIG. 1  is a schematic diagram illustrating a structure of a thin film solar battery in the present disclosure; and 
         FIG. 2  is a schematic diagram illustrating a preparation process of a thin film solar battery in 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 a plurality of serial/parallel battery cells can be formed in the P1, P2, and P3 etching processes, regions disabling photoelectrical conversion (including regions that corresponds to etching lines of the P1, P2, and P3 etching processes and spaced regions between adjacent etching lines thereof), i.e., the so-called “dead zone” in the thin film solar battery, will be produced on the thin film solar battery. 
     The P1, P2 and P3 etching processes are implemented by the laser or mechanical etching, which is limited by the technical level of the existing etching process and the cost control factors, so the width and accuracy of P1-P3 etching lines are hard to improve significantly, causing a difficulty in effective reduction of an area of the dead zone, and finally affecting the light conversion efficiency of the thin film solar battery. 
     Referring to  FIG. 1 , some embodiments of the present disclosure provide a thin film solar battery. The thin film solar battery comprises a substrate  10  and a plurality of serial battery cells disposed in interval on the substrate  10 . Each of the plurality of battery cells comprises a back electrode layer  20 , a light absorption layer  30 , a buffer layer  40 , and an upper electrode layer  50  disposed sequentially. A first groove  60  passing through the back electrode layer  20  is disposed between the back electrode layers  20  of any two adjacent battery cells in the plurality of battery cells. The first groove  60  is filled with an insulator  70 , such that the back electrode layers  20  of the two adjacent battery cells are insulated from each other. Each of the plurality of battery cells is provided with a second groove  80  passing through the light absorption layer  30  and the buffer layer  40 . The upper electrode layer  50  of one battery cell covers the buffer layer  40  of the one battery cell and extends to the second groove  80  of the one battery cell, so as to contact the back electrode layer  20  of another adjacent battery cell, thereby serially connecting the two adjacent battery cells. A third groove  90  is arranged between any two adjacent battery cells, and the third groove  90  insulates the upper electrode layers  50  of the two adjacent battery cells from each other. 
     The thin film solar battery has the following advantages: since the first groove  60  is provided with the insulator  70 , the second groove  80  can be formed above a partial surface of the insulator  70 , i.e., the position of the second groove  80  partially overlaps the position of the first groove  60  therefore the spacing distance between the second groove  80  and the first groove  60  is reduced. The area of the dead zone is greatly reduced in this manner, and thereby the conversion efficiency of the thin film solar battery component is greatly improved. 
     In some embodiments of the present disclosure, the insulator  70  is arranged at a position where the first etching line (i.e., P1 etching) of the thin film solar battery is located, so as to perform a second etching (i.e., P2 etching) at a corresponding position of a partial surface of the insulator  70 , thereby reducing the area of the dead zone. 
     In a preparation method of the thin film solar battery provided in some embodiments of the present disclosure, the first groove  60  is formed in the first etching process, and the insulator  70  is formed via a mask in the first groove  60 , so as to perform a second etching process at a corresponding position of a partial surface of the insulation section  70 . Thus the spacing distance between the position of the first etching process and the position of the second etching process is reduced, and accordingly the area of the dead zone is greatly reduced. This method also has the advantages of simple process, high efficiency, and controllability. 
     Referring to  FIG. 1 , a first battery cell  100  and a second battery cell  200  disposed adjacent to each other in the thin film solar battery are used as an example below to describe the structure of the thin film solar battery. 
     The first battery cell  100  and the second battery cell  200  are adjacent to each other and have the same structure. That is, the first battery cell  100  and the second battery cell  200  are actually repetitive battery cells with the same structure, and they are named differently only for the purpose of better explaining the relationship between the elements in the two adjacent battery cells. The first battery cell  100  comprises a first back electrode layer  21 , a first light absorption layer  81 , a first buffer layer  41 , and a first upper electrode layer  51  arranged sequentially. The second battery cell  200  comprises a second back electrode layer  22 , a second light absorption layer  32 , a second buffer layer  42 , and a second upper electrode layer  52  arranged sequentially. The first battery cell  100  and the second battery cell  200  share the substrate  10 . The first back electrode layer  21  and the second back electrode layer  22  are isolated from each other by the insulator  70 . Referring to  FIG. 2 , the first light absorption layer  31  and the first buffer layer  41  have the second groove  80  in a direction of thicknesses of the first light absorption layer  31  and the first buffer layer  41  and passing through the first light absorption layer  31  and the first buffer layer  41 . Referring to  FIG. 1 , the first upper electrode layer  51  covers the first buffer layer  41  and extends to the second groove  80  to cover a part of the second back electrode layer  22 , so as to electrically connect the second back electrode layer  22 , i.e., the first battery cell  100  and the second battery cell  200  are electrically connected with each other in series. 
     In some embodiments of the present disclosure, a portion of the first upper electrode layer  51  that extends to the second groove  80  covers the insulator  70 . In some other embodiments of the present disclosure, a portion of the first upper electrode layer  51  that extends to the second groove  80  does not cover the insulator  70 . That is, the first groove  60  formed by the first etching (P1 etching) and the second groove  80  may or may not overlap. 
     In some embodiments of the present disclosure, a portion of the back electrode layer and a portion of each of the plurality of insulation sections are exposed from the bottom of each of the plurality of second grooves. 
     In some embodiments of the present disclosure, as shown in  FIG. 1 , the bottom of the second groove  80  of the first battery cell  100  is located at a boundary between the insulator  70  of the first battery cell  100  and the back electrode layer  22  of the adjacent second battery cell  200 , and the upper electrode layer  51  located in the second groove  80  covers partial insulator  70  of the first battery cell  100  and partial back electrode layer  22  of the adjacent second battery cell  200 . At this time, the upper electrode layer  51  is extended to the second groove  80 , and a width of the portion overlapping the insulator  70  is expressed by d 1 . A width of the insulator  70  is expressed by m. In some embodiments of the present disclosure, m and d 1  satisfy the condition below: m&gt;d 1 &gt;0. The reason why m&gt;d 1  is defined is that if the portion of the first upper electrode layer  51  that extends to the second groove  80  comes into contact with the first back electrode layer  21 , a short circuit will occur. In some embodiments, m and d 1  satisfy the condition below: m−d 1 ≥30 μm, which can better avoid such short circuits. The insulator  70  isolates and thereby insulates the first back electrode layer  21  from the second back electrode layer  22 , thus achieving relative independence between the first battery cell  100  and the second battery cell  200 . In some embodiments of the present disclosure, the width m of the insulator  70  satisfies the condition below: 30 μm≤m≤60 μm, which can achieve a better insulation effect. 
     In some embodiments of the present disclosure, material of the insulator  70  includes at least one of Si 3 N 4 , AlN, SiO 2 , and Al 2 O 3 . For example, the material of the insulator  70  is Si 3 N 4 . In some other embodiments of the present disclosure, material of the insulator  70  includes more than one of Si 3 N 4 , AlN, SiO 2  and Al 2 O 3 . For example, the material of the insulator  70  is a compound film of Si 3 N 4  and SiO 2 . 
     A width of the second groove  80  may be of any size. In some embodiments of the present disclosure, however, to better connect with electrodes (such as electrodes in the back electrode layer and the upper electrode layer) and considering reducing the size of the dead zone, the width of the second groove  80  is 50 μm˜80 μm, which may better connect with the electrodes and reduce the size of the dead zone. 
     In some embodiments of the present disclosure, the first battery cell  100  and the second battery cell  200  are isolated from each other by the third groove  90 . The third groove  90  isolates the first upper electrode layer  51  from the second upper electrode layer  52 , isolates the first buffer layer  41  from the second buffer layer  42 , and isolates the first light absorption layer  31  from the second light absorption layer  32 . 
     The third groove  90  cooperates with the insulator  70  to achieve “relative independence” between the first battery cell  100  and the second battery cell  200 . The reason why we say “relative independence” is that the first upper electrode layer  51  in the second groove  80  realizes a serial connection between the first battery cell  100  and the second battery cell  200 . 
     The substrate  10  may be made from any material, including glass, stainless steel, and flexible material. A thickness of the substrate  10  is also not limited. The substrate  10  plays a role of supporting the solar battery. 
     Material of the back electrode layer  20  may be Mo, Ti, Cr, Cu, or the back electrode layer  20  may be a transparent conductive layer. The transparent conductive layer includes one or more of aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (AZO), and indium-doped tin oxide (ITO). A thickness of the back electrode layer  20  may not be limited. In some embodiments of the present disclosure, the thickness of the back electrode layer  20  is 200 nm˜800 nm. In some other embodiments of the present disclosure, the thickness of the insulator  70  is the same as the thickness of the back electrode layer  20 . In some other embodiments of the present disclosure, the thickness of the insulator  70  is greater than the thickness of the back electrode layer  20  to effectively avoid a formation of a short circuit. 
     Material of the light absorption layer  30  is one of copper indium gallium selenium, copper indium selenium, and copper indium gallium sulfur. A thickness of the light absorption layer  30  may not be limited, and in some embodiments of the present disclosure, it may be 0.5 μm˜3 μm. 
     Material of the buffer layer  40  is one of zinc sulfide, cadmium sulfide and indium sulfide. A thickness of the buffer layer  40  may not be limited, and in some embodiments, it is 30 nm˜100 nm. 
     The upper electrode layer  50  is one of transparent conductive layers of AZO, BZO, ITO. A thickness of the upper electrode layer  50  may not be limited, and in some embodiments, it is 100 nm˜1 μm. 
     In some embodiments of the present disclosure, other functional layers such as a zinc oxide layer and a zinc magnesium oxide layer can be added between any two of the back electrode layer, the light absorption layer, the buffer layer, and the upper electrode layer to facilitate close cohesion between layers and help the absorption and conversion of light. 
     Referring to  FIG. 2 , some embodiments of the present disclosure further provide a preparation method of a thin film solar battery. The preparation method comprises the following steps: 
     a) providing a substrate  10 , forming a back electrode layer  20  on the substrate  10 , and performing a first etching of the back electrode layer  20  to form on the back electrode layer  20  a plurality of first grooves  60  passing through the back electrode layer  200 ; 
     b) forming an insulator  70  in each of the plurality of first grooves  60 , thereby forming a plurality of insulators; 
     c) forming a light absorption layer  30  and a buffer layer  40  sequentially on a surface of the back electrode layer  20  formed with the plurality of insulators  70 , performing a second etching of the light absorption layer  30  and the buffer layer  40  to form a plurality of second grooves  80  passing through the light absorption layer  30  and the buffer layer  40 ; and 
     d) forming an upper electrode layer  50  on a surface of the buffer layer  40 , the upper electrode layer  50  extending to the plurality of second grooves  80 , and performing a third etching of the upper electrode layer  50 , the buffer layer  40 , and the light absorption layer  30  to form a plurality of third grooves  90  passing through the upper electrode layer  50 , the buffer layer  40 , and the light absorption layer  30 , so as to obtain a plurality of serially connected battery cells. 
     For the description of the light absorption layer  30 , reference can be made to the descriptions of the first light absorption layer  31  and the second light absorption layer  32 . For the description of the buffer layer  40 , reference can be made to the descriptions of the first buffer layer  41  and the second buffer layer  42 . For the description of the upper electrode layer  50 , reference can be made to the descriptions of the first upper electrode layer  51  and the second upper electrode layer  52 . These will not be elaborated here. 
     In step a), the method for forming the back electrode layer  20  may be a method of chemical vapor deposition, magnetron sputtering, and atomic layer deposition, etc. After the first etching, the back electrode layer  20  can be divided into a plurality of “sub back electrode layers” disposed in interval which are similar to the first back electrode layer  21 , the second back electrode layer  22 , etc. The “sub back electrode layers”, for example, are the first back electrode layer  21  and the second back electrode layer  22  as shown in  FIG. 1 . The second and third etching in steps c) and d) are to engrave the light absorption layer  30 , the buffer layer  40 , and the upper electrode layer  50  to form battery cells relatively independent from and serially connected with each other. The first battery cell  100  and the second battery cell  200  shown in  FIG. 1  are named for the purpose of better explaining the relationship between the elements in the two adjacent battery cells. In fact, the first battery cell  100  and the elements thereof have the same structures as the second battery cell  200  and the elements thereof. 
     In step b), a mask is provided (not shown in the drawings), and an insulator  70  is formed in the first groove  60  through the mask. The method for forming the insulator  70  may be any method of magnetron sputtering, spin coating, spraying and chemical vapor deposition. The process of the method of spin coating and spraying is as follows: mixing insulating materials and solvents such as ethanol or water to obtain a mixture, then spin coating or spraying the mixture, and then drying the mixture to obtain the insulator  70 . In some embodiments, the insulation section  70  is formed in the method of magnetron sputtering. 
     In step c), a second etching is performed to the light absorption layer  30  and the buffer layer  40  to form the second groove  80 . The second groove  80  formed by the second etching may partially overlap the first groove  60  formed by the first etching; the second groove  80  may be also isolated from the first groove  60 , i.e., they do not overlap. In some embodiments, the second groove  80  and the first groove  60  partially overlap, i.e., partial surface of the insulator  70  is made to be exposed by the second groove  80 . 
     A width of the insulator  70  is expressed by m. A width of the portion of the insulator  70  that is exposed through the second groove  80  is expressed by d 1 , and in some embodiments of the present disclosure, the width m of the insulator  70  is greater than d 1 , e.g. m−d 1 ≥30 μm. 
     In steps a), c), and d), the first, second, and third etching can all be implemented through mechanical or laser etching. In some embodiments of the present disclosure, the method of the first etching is laser etching; the second and third etching are mechanical etching. Widths of the openings of the formed first groove  60 , second groove  80 , and third groove  90  are not limited. In some embodiments of the present disclosure, widths of the second groove  80  and the third groove  90  may be 60 μm˜80 μm. In some other embodiments of the present disclosure, the spacing distance between the second groove  80  and the third groove  90  is greater than 30 μm. 
     The thin film solar battery and the preparation method thereof have the following advantages: 
     Since the first groove  60  formed by the first etching is provided with the insulator  70 , i.e., the back electrode layers in a plurality of battery cells are disposed in interval by the insulators  70 , thereby the second etching can be performed above a partial surface of the insulators  70 , The second etching forms the second groove  80 , the insulator  70  can be made to be exposed by the second groove  80 ; the spacing distance between the position of the second etching and the position of the first etching is reduced, and accordingly the area of the dead zone is greatly reduced, and thereby the conversion efficiency of the thin film solar battery is greatly improved. 
     This preparation method has the advantages of simple process, high efficiency, and controllability. 
     The thin film solar battery and the preparation method thereof are further described below with reference to the illustrative examples. 
     EXAMPLE 1 
     Example 1 provides a thin film solar battery and a preparation method thereof. The preparation method of the thin film solar battery is as follows: 
     a) providing a substrate and forming a back electrode layer thereon via the method of magnetron sputtering, and performing a first etching of the back electrode layer to form on the back electrode layer a plurality of first grooves passing through the back electrode layer. 
     The material of the substrate is glass, the back electrode layer is a metal Mo layer, and parameters in the method of magnetron sputtering are as follows: taking argon as a gas source and metal Mo as a target material, the vacuum degree being 0.1 Pa˜0.7 Pa; the first etching is laser etching, and the width of the first groove is about 60 μm; 
     b) providing a mask, and forming a plurality of insulators made from Si 3 N 4  in the plurality of first grooves in one-to-one correspondence via the method of magnetron sputtering; 
     c) forming a light absorption layer and a buffer layer sequentially on a surface of the back electrode layer formed with the plurality of insulators, performing a second etching of the light absorption layer and the buffer layer to form a plurality of second grooves passing through the light absorption layer and the buffer layer, wherein the second etching is mechanical etching, the width of the second groove formed by the second etching is about 50 μm, the width d 1  of the portion of the insulator that is made to be exposed by the second groove is about 30 μm, the light absorption layer is a copper indium gallium selenide compound layer having a thickness of about 3 μm, and the buffer layer is a cadmium sulfide layer having a thickness of about 80 nm; 
     d) forming an upper electrode layer on a surface of the buffer layer, the upper electrode layer extending to the second grooves, and performing a third etching of the upper electrode layer, the buffer layer, and the light absorption layer to form a plurality of third grooves passing through the upper electrode layer, the buffer layer, and the light absorption layer, so as to obtain a plurality of serially connected battery cells, wherein the third etching is mechanical etching, the spacing distance (i.e., the distance between right border of the second groove and left border of the adjacent third groove) between the third groove and the second groove is 40 μm, the upper electrode layer is an AZO transparent thin conductive film having a thickness of about 800 nm, and the width of the third groove is about 60 μm. 
     The width between the first groove and the third groove (i.e., the width between left border of the first groove and right border of the adjacent third groove, the same below) in the obtained thin film solar battery is about 180 μm. 
     EXAMPLE 2 
     Example 2 provides a thin film solar battery and a preparation method thereof. The preparation method of the thin film solar battery is as follows: 
     a) providing a substrate and forming a back electrode layer thereon via the method of magnetron sputtering, and performing a first etching of the back electrode layer to form on the back electrode layer a plurality of first grooves passing through the back electrode layer. 
     The material of the substrate is glass, the back electrode layer is a metal Mo layer, and parameters in the method of magnetron sputtering are as follows: taking argon as a gas source and metal Mo as a target material, the vacuum degree being 0.1 Pa˜0.7 Pa; the first etching is laser etching, and the width of the first groove is about 50 μm; 
     b) providing a mask, and forming a plurality of insulators made from Si 3 N 4  in the plurality of first grooves in one-to-one correspondence via the method of magnetron sputtering; 
     c) forming a light absorption layer and a buffer layer sequentially on a surface of the back electrode layer formed with the plurality of insulators, performing a second etching of the light absorption layer and the buffer layer to form a plurality of second grooves passing through the light absorption layer and the buffer layer, wherein the second etching is mechanical etching, the width of the second groove is about 70 μm, the width d 1  of the portion of the insulator that is made to be exposed by the second groove is about 15 μm, the light absorption layer is a copper indium gallium selenide compound layer having a thickness of about 3 μm, and the buffer layer is a cadmium sulfide layer having a thickness of about 80 nm; 
     d) forming an upper electrode layer on a surface of the buffer layer, the upper electrode layer extending to the second grooves, and performing a third etching of the upper electrode layer, the buffer layer, and the light absorption layer to form a plurality of third grooves passing through the upper electrode layer, the buffer layer, and the light absorption layer, so as to obtain a plurality of serially connected battery cells, wherein the third etching is mechanical etching, the spacing distance between the third groove and the second groove is 40 μm, the upper electrode layer is an AZO transparent thin conductive film having a thickness of about 30 μm, and the width of the third groove is about 70 μm. 
     The preparation method of a thin film solar battery in Example 2 is substantially the same as that in Example 1, and their difference lies in the width d 1  of the portion of the insulator that is made to be exposed by the second groove, and the widths of the first, second and third grooves. 
     The width between the first groove and the third groove in the obtained thin film solar battery is about 215 μm. 
     EXAMPLE 3 
     Example 3 provides a thin film solar battery and a preparation method thereof. The preparation method of the thin film solar battery is as follows: 
     a) providing a substrate and forming a back electrode layer thereon via the method of magnetron sputtering, and performing a first etching of the back electrode layer to form on the back electrode layer a plurality of first grooves passing through the back electrode layer. 
     The material of the substrate is glass, the back electrode layer is a metal Mo layer, and parameters in the method of magnetron sputtering are as follows: taking argon as a gas source and metal Mo as a target material, the vacuum degree being 0.1 Pa˜0.7 Pa; the first etching is laser etching, and the width of the first groove is about 40 μm; 
     b) providing a mask, and forming a plurality of insulators made from Si 3 N 4  in the plurality of first grooves in one-to-one correspondence via the method of magnetron sputtering; 
     c) forming a light absorption layer and a buffer layer sequentially on a surface of the back electrode layer formed with the plurality of insulators, performing a second etching of the light absorption layer and the buffer layer to form a plurality of second grooves passing through the light absorption layer and the buffer layer, wherein the second etching is mechanical etching, the width of the second groove is about 80 μm, the width d 1  of the portion of the insulator that is made to be exposed by the second groove is about 5 μm, the light absorption layer is a copper indium gallium selenide compound layer having a thickness of about 3 μm, and the buffer layer is a cadmium sulfide layer having a thickness of about 80 nm; 
     d) forming an upper electrode layer on a surface of the buffer layer, the upper electrode layer extending to the second grooves, and performing a third etching of the upper electrode layer, the buffer layer, and the light absorption layer to form a plurality of third grooves passing through the upper electrode layer, the buffer layer, and the light absorption layer, so as to obtain a plurality of serially connected battery cells, wherein the third etching is mechanical etching, the spacing distance between the third groove and the second groove is 40 μm, the upper electrode layer is an AZO transparent thin conductive film having a thickness of about 30 μm, and the width of the third groove is about 80 μm. 
     The preparation method of a thin film solar battery in Example 3 is substantially the same as that in Example 1, but the width d 1  of the portion of the insulator that is made to be exposed by the second groove, and the widths of the first, second and third grooves are different. 
     The width between the first groove and the third groove in the obtained thin film solar battery is about 235 μm. 
     EXAMPLE 4 
     Example 4 provides a thin film solar battery and a preparation method thereof. The preparation method of the thin film solar battery is as follows: 
     a) providing a substrate and forming a back electrode layer thereon via the method of magnetron sputtering, and performing a first etching of the back electrode layer to form on the back electrode layer a plurality of first grooves passing through the back electrode layer. 
     The material of the substrate is glass, the back electrode layer is a metal Mo layer, and parameters in the method of magnetron sputtering are as follows: taking argon as a gas source and metal Mo as a target material, the vacuum degree being 0.1 Pa˜0.7 Pa; the first etching is laser etching, and the width of the first groove is about 40 μm; 
     b) providing a mask, and forming a plurality of insulators made from Si 3 N 4  in the plurality of first grooves in one-to-one correspondence via the method of magnetron sputtering; 
     c) forming a light absorption layer and a buffer layer sequentially on a surface of the back electrode layer formed with the plurality of insulators, performing a second etching of the light absorption layer and the buffer layer to form a plurality of second grooves passing through the light absorption layer and the buffer layer, wherein the second etching is mechanical etching, the width of the second groove is about 60 μm, the insulator is not exposed from the second groove (i.e., the width d 1  of the portion of the insulator that is made to be exposed by the second groove is 0), the spacing distance between the second groove and the first groove is 10 μm, the light absorption layer is a copper indium gallium selenide compound layer having a thickness of about 3 μm, and the buffer layer is a cadmium sulfide layer having a thickness of about 80 nm; 
     d) forming an upper electrode layer on a surface of the buffer layer, the upper electrode layer extending to the second grooves, and performing a third etching of the upper electrode layer, the buffer layer, and the light absorption layer to form a plurality of third grooves passing through the upper electrode layer, the buffer layer, and the light absorption layer, so as to obtain a plurality of serially connected battery cells, wherein the third etching is mechanical etching, the spacing distance between the third groove and the second groove is 40 μm, the upper electrode layer is an AZO transparent thin conductive film having a thickness of about 30 μm, and the width of the third groove is about 60 μm. 
     The preparation method of a thin film solar battery in Example 4 is substantially the same as that in Example 1, but in Example 4, the position of the first etching is isolated from the position of the second etching, i.e., in step c) of Example 4, after the second etching, the insulator is not exposed by the second groove. In addition, the width of the first groove in Example 4 is also different from that in Example 1. 
     The width between the first groove and the third groove in the obtained thin film solar battery is about 210 μm. 
     To better demonstrate the excellent performance of the thin film solar battery in the present disclosure, the present disclosure also provides a comparative example. 
     COMPARATIVE EXAMPLE 
     This comparative example provides a thin film solar battery and a preparation method thereof. The preparation method of the thin film solar battery is as follows: 
     a) providing a substrate and forming a back electrode layer thereon via the method of magnetron sputtering, and performing a first etching of the back electrode layer to form on the back electrode layer a plurality of first grooves passing through the back electrode layer. 
     The material of the substrate is glass, the back electrode layer is a metal Mo layer, and parameters in the method of magnetron sputtering are as follows: taking argon as a gas source and metal Mo as a target material, the vacuum degree being 0.1 Pa˜0.7 Pa; the first etching is laser etching, and the width of the first groove is about 60 μm; 
     b) forming a light absorption layer and a buffer layer sequentially on a surface of the back electrode layer formed with a plurality of first grooves, performing a second etching of the light absorption layer and the buffer layer to form a plurality of second grooves passing through the light absorption layer and the buffer layer, wherein the second etching is mechanical etching, the width of the second groove is about 60 μm, the spacing distance between the second groove and the first groove is 40 μm, the light absorption layer is a copper indium gallium selenide compound layer having a thickness of about 3 μm, and the buffer layer is a cadmium sulfide layer having a thickness of about 80 nm; 
     c) forming an upper electrode layer on a surface of the buffer layer, the upper electrode layer extending to the second grooves, and performing a third etching of the upper electrode layer, the buffer layer, and the light absorption layer to form a plurality of third grooves passing through the upper electrode layer, the buffer layer, and the light absorption layer, so as to obtain a plurality of serially connected battery cells, wherein the third etching is mechanical etching, the upper electrode layer is an AZO transparent thin conductive film having a thickness of about 800 nm, the width of the third groove is about 60 μm, and the spacing distance between the third groove and the second groove is 40 μm. 
     The preparation method of thin film solar battery in this comparative example is substantially the same as that in Example 4, and their difference lies in that the comparative example does not include the step of forming an insulator in the first groove, i.e., in this comparative example, the light absorption layer is formed directly on the back electrode layer, i.e., the first groove is filled with the light absorption layer. 
     The width between the first groove and the third groove in the obtained thin film solar battery is about 260 μm. As can be seen, compared with Example 1, the comparative example has a larger area of dead zone. As can be seen from the above Examples 1-4, the area of the dead zone of the thin film solar battery can be greatly reduced; therefore, the photoelectric conversion efficiency of the thin film solar battery can be significantly improved in use. 
     The widths of the above-described 3 grooves can be adjusted according to the implementation process, and is not limited to the above sizes, and the technical features in the above embodiments can be combined in any combination. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but all of them shall be considered within the scope of disclosure of the specification, as long as they do not conflict with each other. The above embodiments are merely some of embodiments of the present disclosure, and the description is specific and detailed, but it should not be understood thereby that they constitute a limitation to the patent scope of the present disclosure. It should be noted that for persons with common skill in the art, various changes and modifications can be made therein without departing from the spirit and essence of the disclosure, which are also considered to be within the scope of the disclosure. Therefore, the protection scope of the patent of the present disclosure shall be determined by the appended claims.