Patent Publication Number: US-2019198690-A1

Title: Processing method for photovoltaic cell and string welding and curing device for photovoltaic cell

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the priority of the Chinese patent application No. 201711396039.X, filed on Dec. 21, 2017, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the technical field of solar cells, in particular to a processing method for a photovoltaic cell and a string welding and curing device for a photovoltaic cell. 
     BACKGROUND 
     With the depletion of natural resources such as petroleum and coal on the earth, development of new natural resources has become an urgent task. At present, solar energy has become the focus of development due to its advantage of cleanness. 
     In main aspect of the use of solar energy, sunlight radiation is converted through the solar cells into electricity, heat, and other energies that humans can utilize. High-efficiency heterojunction solar cells have become the focus of development due to their advantages of high efficiency. When preparing a heterojunction solar cell, it is necessary to firstly prepare a cell sheet. After the cell sheet is completed, multiple cell sheets are string welded into a string of cell sheets through a solder ribbon. Finally, the string of cell sheets is packaged with a back plate, a front plate and other packaging materials, and the entire heterojunction solar cell is completed. 
     In the above processes for preparing a heterojunction solar cell, the last process for preparing the cell sheet is generally as follows: printing a silver paste electrode, and then drying and curing the silver paste. After the cell sheets are completed, the string welding process of the cell sheets immediately follows. At present, infrared heating is required when silver paste is cured, and infrared heating is also required when the string welding is performed. 
     At present, the silver paste curing of the cell sheet and the string welding of the cell sheet are respectively performed with infrared heating, resulting in waste of resources, as well as prolonged processing time and reduced production efficiency. 
     SUMMARY 
     The objective of the present disclosure is to provide a processing method for a photovoltaic cell and a string welding and curing device for a photovoltaic cell, to solve the above problems, save resources, shorten processing time, and increase production efficiency. 
     The present disclosure provides a processing method for a photovoltaic cell, including: 
     Step S 1 : plating both side surfaces of a monocrystalline silicon wafer; 
     Step S 2 : forming a first electrode on one side surface of the plated monocrystalline silicon wafer; 
     Step S 3 : forming a second electrode on the other side surface of the plated monocrystalline silicon wafer, to form a cell sheet; and 
     Step S 4 : string welding a plurality of cell sheets and at the same time, curing the first electrode and the second electrode, by using a string welding and curing device for a photovoltaic cell. 
     In the processing method for a photovoltaic cell described above, preferably, step S 1  specifically includes: 
     Step S 11 : texturing and cleaning the both side surfaces of the monocrystalline silicon wafer; 
     Step S 12 : depositing a first intrinsic passivation layer and a first amorphous silicon doped layer on one side surface of the monocrystalline silicon wafer in sequence; depositing a second intrinsic passivation layer and a second amorphous silicon doped layer on the other side surface of the monocrystalline silicon wafer in sequence; and 
     Step S 13 : depositing a first transparent conductive layer on the first amorphous silicon doped layer; depositing a second transparent conductive layer on the second amorphous silicon doped layer. 
     In the processing method for a photovoltaic cell described above, preferably, step S 2  specifically includes: 
     Step S 21 : forming a first electrode by screen printing a mixed solution of silver and resin on the first transparent conductive layer; and 
     Step S 22 : drying the first electrode. 
     In the processing method for a photovoltaic cell described above, preferably, step S 3  specifically includes: 
     Step S 31 : performing a first screen printing of a mixed solution of silver and resin on the second transparent conductive layer, to form a base layer of the second electrode; 
     Step S 32 : drying the base layer of the second electrode; 
     Step S 33 : performing a second screen printing of a mixed solution of silver and resin on the base layer of the second electrode, to form the second electrode; and 
     Step S 34 : drying the second electrode. 
     In the processing method for a photovoltaic cell described above, preferably, step S 4  specifically includes: 
     Step S 41 : arranging the plurality of cell sheets at intervals on a conveying device, and placing a solder ribbon between adjacent cell sheets, with one end of the solder ribbon contacting the first electrode of one cell sheet and the other end of the solder ribbon contacting the second electrode of an adjacent cell sheet at a side; 
     Step S 42 : pressing tightly the solder ribbon and the cell sheets together with a pressing pin; and 
     Step S 43 : heating, by a heating device, the solder ribbon and the electrodes of the cell sheets so that they are welded to form a string of cell sheets, and at the same time, curing the first electrode and the second electrode. 
     In the processing method for a photovoltaic cell described above, preferably, in step S 43 , the heating device includes a first heating component disposed above the conveying device and a second heating component disposed below the conveying device; and 
     Step S 43  specifically includes: turning on the first heating component and the second heating component, to heat the solder ribbon, an upper surface and a lower surface of the cell sheet simultaneously, such that the solder ribbon, and the electrodes of the cell sheet are welded to form the plurality of cell sheets in series, and the first electrode and the second electrode are cured. 
     In the processing method for a photovoltaic cell described above, preferably, step S 43  further includes: controlling the heating device to cure the first electrode and the second electrode of the cell sheet at a temperature between 150 and 230 degrees Celsius for 20 to 40 minutes. 
     In the processing method for a photovoltaic cell described above, preferably, in step S 12 , the first intrinsic passivation layer and the first amorphous silicon doped layer are deposited on one side surface of the monocrystalline silicon wafer in sequence, and the second intrinsic passivation layer and the second amorphous silicon doped layer are deposited on the other side surface of the monocrystalline silicon wafer in sequence, by using plasma-enhanced chemical vapor deposition or hot filament chemical vapor deposition. 
     In the processing method for a photovoltaic cell described above, preferably, in step S 13 , the first transparent conductive layer is deposited on the first amorphous silicon doped layer and the second transparent conductive layer is deposited on the second amorphous silicon doped layer, by using physical vapor deposition. 
     The present disclosure also provides a string welding and curing device for a photovoltaic cell, including: 
     a conveying device; 
     a first heating component including an infrared heater and a hot air device, wherein both the infrared heater and the hot air device are provided above a conveying surface of the conveying device, and can be raised and lowered; and 
     a pressing pin, wherein the pressing pin is provided above the conveying surface of the conveying device, and can be raised and lowered. 
     Preferably, the string welding and curing device for a photovoltaic cell described above also includes a support stand, wherein the support stand is provided above the conveying surface of the conveying device, and can be raised and lowered; and 
     the infrared heater, the hot air device and the pressing pin are all fixedly connected to the support stand. 
     Preferably, the string welding and curing device for a photovoltaic cell described above also includes an electric lifting device, wherein the electric lifting device includes a lifting plate; the lifting plate is disposed above the conveying surface of the conveying device; the lifting plate can be moved toward or away from the conveying device; and the support stand is fixed on the lifting plate. 
     In the string welding and curing device for a photovoltaic cell described above, preferably, the electric lifting device also includes a driving member, and a driving end of the driving member is fixedly connected to the lifting plate. 
     Preferably, the string welding and curing device for a photovoltaic cell described above also includes a second heating component, wherein the second heating component is disposed on the conveying device on one side of the conveying device facing away from the conveying surface. 
     Preferably, the string welding and curing device for a photovoltaic cell described above also includes a support platform for supporting the conveying device, wherein the support platform is disposed below the conveying device; and the second heating component is fixed on the support platform. 
     The present disclosure provides a processing method for a photovoltaic cell, including step S 1 : plating both side surfaces of a monocrystalline silicon wafer; Step S 2 : forming a first electrode on one side surface of the plated monocrystalline silicon wafer; Step S 3 : forming a second electrode on the other side surface of the plated monocrystalline silicon wafer, to form a cell sheet; and Step S 4 : string welding a plurality of cell sheets and at the same time, curing the first electrode and the second electrode, by using a string welding and curing device for a photovoltaic cell. With the processing method provided by the present disclosure, the electrodes on the cell sheets can be cured while the cell sheets are string welded. It can save resources, shorten the processing time of the photovoltaic cell, and improve the production efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of a processing method for a photovoltaic cell according to an embodiment of the present disclosure; 
         FIG. 2  is a front view of a string welding and curing device for a photovoltaic cell according to an embodiment of the present disclosure; 
         FIG. 3  is a side perspective view of a string welding and curing device for a photovoltaic cell according to an embodiment of the present disclosure. 
     
    
    
     REFERENCE NUMERALS 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 10-Conveying device 
                 20 - Lifting plate 
               
               
                   
                 21 - Connecting protrusion 
                 30 - First heating component 
               
               
                   
                 40-Pressing pin 
                 50-Support stand 
               
               
                   
                 60-Support platform 
               
               
                   
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail. Examples of the embodiments are shown in the accompanying drawings. The same or similar reference numerals throughout the drawings denote the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the drawings are exemplary, are used to explain the present disclosure, and cannot be construed as limiting the present disclosure. 
     As shown in  FIG. 1 , the present disclosure provides a processing method for a photovoltaic cell, including the following steps. 
     In step S 1 , both side surfaces of a monocrystalline silicon wafer are plated. The plating specifically includes the following steps. 
     In Step S 11 , the both side surfaces of a monocrystalline silicon wafer are textured and cleaned. Texturing is to form pyramidal suede surfaces on the both side surfaces of a monocrystalline silicon wafer, and the size of the pyramid is 1 to 10 microns. Texturing can reduce reflection on the surface of the monocrystalline silicon wafer, and thereby increase the conversion rate of the solar cell sheet. 
     In Step S 12 , a first intrinsic passivation layer and a first amorphous silicon doped layer are deposited on one side surface of the monocrystalline silicon wafer in sequence; a second intrinsic passivation layer and a second amorphous silicon doped layer are deposited on the other side surface of the monocrystalline silicon wafer in sequence. Specifically, the above intrinsic passivation layers and the amorphous silicon doped layers may be deposited on the two side surfaces of the monocrystalline silicon wafer by plasma-enhanced chemical vapor deposition (PECVD) or hot filament chemical vapor deposition (HWCVD). The two intrinsic passivation layers and the two amorphous silicon doped layers are formed in the same manner, deposited in different chambers, and can be processed in the same step. Preferably, the first amorphous silicon doped layer is an N-type amorphous silicon base layer, the second amorphous silicon doped layer is a P-type amorphous silicon base layer; and the first intrinsic passivation layer and the second intrinsic passivation layer are both amorphous silicon based intrinsic layers. 
     In Step S 13 , a first transparent conductive layer is deposited on the first amorphous silicon doped layer; a second transparent conductive layer is deposited on the second amorphous silicon doped layer. Specifically, the first transparent conductive layer and the second transparent conductive layer may be prepared by physical vapor deposition (PVD), or may be prepared by remote plasma coating (RPD). Preferably, the above first transparent conductive layer and the second transparent conductive layer are both TCO glass layers. 
     In Step S 2 , a first electrode is formed on one side surface of the plated monocrystalline silicon wafer. Specifically, the first electrode is formed on the first transparent conductive layer. Preferably, a plurality of first fine gate lines and a first main gate line may be printed on the first transparent conductive layer by screen printing. The first fine gate lines and the first main gate line constitute the first electrode. It should be understood by those skilled in the art that, since the electrodes of the cell sheet are mostly made of mixed solution of silver paste and resin, the first electrode has to be dried after the first electrode is formed. Specifically, a hot air blower can be used for the drying. 
     In Step S 3 , a second electrode is formed on the other side surface of the plated monocrystalline silicon wafer, to form a cell sheet. Specifically, a second electrode is formed on the second transparent conductive layer to form a cell sheet. Further, both the first electrode and the second electrode are both made of silver paste and resin. The process of forming the second electrode specifically includes performing a first printing on the second transparent conductive layer by screen printing to form a base layer of the second electrode; drying the base layer of the second electrode; and performing a second printing on the base layer of the second electrode by screen printing to form the second electrode; and finally, drying the second electrode. Specifically, a hot air blower can be used for the drying. 
     More specifically, a plurality of second fine gate lines may be printed on the second transparent conductive layer by screen printing to form the base layer of the second electrode. A plurality of third fine gate lines and a second main gate line are printed on the base layer of the second electrode by screen printing. The third fine gate lines cover the second fine gate lines. Consequently, the second fine gate lines, the third fine gate lines and the second main gate line form the second electrode. 
     Since the processed cell sheet is a bifacially-generated battery, it is necessary to print the electrodes on both side surfaces of a monocrystalline silicon wafer. In practical applications, the silver content of the electrode on the side surface having the larger light-receiving area can be increased in order to increase the electrical conductivity. Therefore, the second electrode is printed twice. The second fine gate line of the base layer of the second electrode formed in the first printing has a thickness equal to the thickness of the first fine gate line of the first electrode. After the twice printings, a total thickness of the second fine gate line and the third fine gate line of the second electrode is twice of the thickness of the first fine gate line of the first electrode, thus greatly improving the electrical conductivity. 
     In Step S 4 , a plurality of cell sheets are string welded and at the same time, the first electrode and the second electrode are cured, by using a string welding and curing device for a photovoltaic cell. The following description is given in connection with the string welding and curing device for a photovoltaic cell as shown in  FIGS. 2 and 3 . 
     The step S 4  specifically includes step S 41 , in which the plurality of cell sheets are arranged at intervals on a conveying device  10 , and a solder ribbon is placed between adjacent cell sheets, with both ends of the solder ribbon respectively connected to the opposite electrodes of the adjacent cell sheets. It should be understood by those skilled in the art that, when the solar cell sheets are arranged, appropriate distances should be maintained, and the number of the arranged sheets may be adjusted according to actual situation. For example,  2  to  12  cell sheets may be arranged on the conveying device  10 , and a solder ribbon is disposed between adjacent cell sheets, with one end of the solder ribbon connected to the first electrode of the first cell sheet, and the other end of the solder ribbon connected to the second electrode of the second cell sheet adjacent to the first cell sheet. 
     In Step S 42 , the solder ribbon and the cell sheets are pressed together with a pressing pin  40 . Specifically, when the solder ribbon and the cell sheets are placed, the pressing pin  40  is moved away from the conveying device  10 , and after the placement is completed, the pressure pin  40  is moved to the connection where the solder ribbon and the cell sheets are pressed together, and the solder ribbon and the cell sheets are pressed tightly and fixed. 
     In Step S 43 , heated by a heating device, the solder ribbon and the electrodes of the cell sheets are welded to form a string of cell sheets, and at the same time, the first electrode and the second electrode are cured. After the solder ribbon and the cell sheets are pressed tightly with the pressing pin  40 , the heating device is started, to heat the cell sheets and the solder ribbon at a temperature of 150-230° C. for 20-40 minutes. For example, the cell sheets and the solder ribbon is heated at a temperature of 150° C. for 40 minutes or at a temperature of 230° C. for 20 minutes. At this time, the solder ribbon and the electrodes of the cell sheets are welded. Therefore, the plurality of cell sheets are successfully connected in series. At the same time, the first electrode and the second electrode on the cell sheet are heated to be cured, thus finishing the process. Since the welding requires a short time, after the pressing pin presses tightly against the solder ribbon and the cell sheets to assist the welding, the pressing pin may be moved upwards away from the solder ribbon and the cell sheets. At this time, the heating device heats the cell sheets and the solder ribbon at a temperature of 150-230° C. for 20-40 minutes, mainly in order to cure the first electrode and the second electrode on the cell sheet. 
     Specifically, in Step S 43 , the heating device includes a first heating component  30  disposed above the conveying device  10  and a second heating component disposed below the conveying device  10 . After the pressing pin  40  presses tightly against the solder ribbon and the cell sheets, the first heating component  30  and the second heating component are turned on, such that the solder ribbon, the upper surface and the lower surface of the cell sheet are heated simultaneously, and at the same time of the string welding, the first electrode and the second electrode are cured. The above first heating component  30  includes an infrared heater and a hot air device, and the second heating component may be a heater of resistance heating sheet. 
     With the processing method provided by the embodiment of the present disclosure, the processing steps of curing the electrodes when processing the cell sheets can be eliminated. Instead, the electrodes on the cell sheets are cured while the cell sheets are string welded, thereby saving resources, shortening the processing time for the photovoltaic cell, and improving production efficiency. It should be understood that after the string welding is completed, there is a conventional packaging process. 
     As shown in  FIG. 2  and  FIG. 3 , an embodiment of the present disclosure further provides a string welding and curing device for a photovoltaic cell, which includes a conveying device  10 , a first heating component  30 , and a pressing pin  40 . 
     The first heating component  30  includes an infrared heater and a hot air device. The infrared heater and the hot air device are provided above the conveying surface of the conveying device  10 , and can be raised and lowered. The pressing pin  40  is provided above the conveying surface of the conveying device  10 , and can be raised and lowered. Preferably, the above-mentioned conveying device  10  is a conveyor belt. 
     During processing, a plurality of cell sheets are arranged at intervals on the conveying device  10 , and the solder ribbon is placed between adjacent cell sheets, with both ends of the solder ribbon respectively connected to the opposite electrodes of the adjacent cell sheets. It should be understood by those skilled in the art that, when the solar cell sheets are arranged, appropriate distances should be maintained, and the number of the arranged sheets may be adjusted according to actual situation. For example, 2 to 12 cell sheets may be arranged on the conveying device  10 , and a solder ribbon is disposed between adjacent cell sheets, with one end of the solder ribbon connected to the second electrode of a first cell sheet, and the other end of the solder ribbon connected to the first electrode of a second cell sheet adjacent to the first cell sheet. 
     Then, the pressing pin  40  and the first heating component  30  are moved downwards approaching the conveying surface of the conveying device  10 , such that the pressing pin  40  presses the solder ribbon and the cell sheets tightly to avoid the movement of the cell sheets and the solder ribbon during the subsequent welding process, which might result in defective welding. Specifically, when the cell sheets and the solder ribbon are placed, the pressing pin  40  is moved away from the conveying device  10 . After the placement is completed, the pressing pin  40  is moved to a position of the cell sheets and the solder ribbon which does not require welding for pressing tightly the solder ribbon and the cell sheets together. 
     Next, after the press pin  40  presses tightly the solder ribbon and the cell sheets, the infrared heater and the hot air device are turned on, such that during the string welding, the first electrode and the second electrode of the cell sheet are cured. 
     In the string welding and curing device for a photovoltaic cell according to the embodiment of the present disclosure, the solder ribbon and the cell sheets are pressed together by the pressing pin  40 , and then by using the first heating component  30 , the string welding of the cell sheets and the solder ribbon is performed, and the first electrode of the cell sheet and the second electrode of the cell sheet are cured. It can allow string welding and curing to be simultaneously performed. It can save resources, shorten the processing time of the photovoltaic cell, and improve production efficiency. 
     When performing string welding and curing, the infrared heater performs a method of concentrated spot heating, and the hot air device blows out hot air to perform full heating of all the cell sheets. The infrared heater and the hot air device are mutually assisted to efficiently and reliably achieve welding and curing. 
     Specifically, the string welding and curing device for a photovoltaic cell provided by the embodiment of the present disclosure also includes an electric lifting device. The electric lifting device includes a lifting plate  20 . The lifting plate  20  is disposed above the conveying surface of the conveying device  10 . The lifting plate  20  can be moved toward or away from the conveying device  10 . The first heating component  30  and the pressing pin  40  are fixedly connected with the lifting plate  20 . 
     Further, the string welding and curing device for a photovoltaic cell provided by the embodiment of the present disclosure also includes a second heating component (not shown in the drawings). The second heating component is disposed on a side of the delivery device  10  away from the conveying surface. Preferably, the second heating component may be a resistance heating sheet and the number thereof is multiple. That is, the first heating component  30  is disposed above the conveying device  10 , and the second heating component is disposed below the conveying device  10 , such that both the upper and lower sides of the cell sheet and the solder ribbon can be heated. 
     In specific application, the electric lifting device is turned on such that the lifting plate  20  drives the pressing pin  40  and the first heating component  30  to move upward away from the conveying surface of the conveying device  10 . Then the plurality of cell sheets are arranged at intervals on the conveying device  10 , and the solder ribbon is placed between adjacent cell sheets, with both ends of the solder ribbon respectively connected to the opposite electrodes of the adjacent cell sheets. 
     Then, the electric lifting device is operated to move the lifting plate  20  downwards to drive the pressing pin  40  and the first heating component  30  to move downwards approaching the conveying surface of the conveying device  10 , such that the pressing pin  40  is moved to a position of the cell sheets and the solder ribbon which does not require welding for pressing them together. 
     Further, the number of the above-mentioned electric lifting devices is two. With two electric lifting devices, it can increase the smoothness of the upward and downward movements of the pressure pin  40  and the first heating component  30 . It can also improve the fixing reliability, and increase the operating safety factor. 
     Next, after the pressing pin  40  presses tightly the solder ribbon and the cell sheets, the first heating component  30  and the second heating component are turned on, such that the solder ribbon, the upper surface of the cell sheet and the lower surface of the cell sheet are simultaneously heated, and while the string welding is performed, the second electrode and the first electrode of the cell sheet are cured. Further, the string welding and curing device for a photovoltaic cell according to an embodiment of the present disclosure also includes a support stand  50 . The support stand  50  is fixedly connected to the two lifting plates  20 . The infrared heater, the hot air device and the pressing pin are all fixed on the support stand  50 . The infrared heater may specifically be an infrared lamp. The heat emitting surface of the infrared lamp faces the conveying surface of the conveying device. The hot air device may be a fan blowing hot air toward the conveying surface of the conveying device. The pressing pin  40  is fixed on the underside of the support stand  50 , and is close to the side of the conveying device  10 . Referring to  FIG. 3 , it can be seen that the support stand  50  is in the form of a cuboid block on which  10  infrared lamps are mounted. When the lifting plate  20  is moved downwards, the pressing pin  40  firstly presses against the cell sheets and the solder ribbon. 
     More specifically, the lifting plate  20  described above is a rectangular plate, and one side of the support stand  50  is fixedly connected to one side of the bottom of the rectangular plate. A connecting protrusion  21  is provided at one end of the lifting plate  20  away from the support stand  50 . 
     The electric lifting device also includes a driving member having a driving end fixedly connected to the lifting plate  20 . Specifically, the driving member is an air cylinder, and the connecting rod of the air cylinder is fixedly connected to the connecting protrusion  21  on the lifting plate  20  so as to control the rising and lowering of the lifting plate  20  to drive the pressing pin  40  and the first heating component  30  to move up and down. 
     Further, the string welding and curing device for a photovoltaic cell provided by the embodiment of the present disclosure also includes a support platform  60  for supporting the conveying device  10 . The support platform  60  is disposed below the conveying device  10 , and the second heating component is fixed on the support platform  60  on one side of the support platform  60  close to the conveying device  10 . The support platform  60  is configured to support the conveying device  10  such that the conveying surface of the conveying device  10  is kept stable during operation, to avoid moving of the cell sheets and the solder ribbon which results in failure of string welding. 
     The structure, features, and effects of the present disclosure have been described in detail with reference to the embodiments shown in the drawings. The above are merely preferred embodiments of the present disclosure, but the present disclosure does not limit the scope of implementation as shown in the drawings. Any equivalent embodiment altered or modified according to the concept of the present disclosure without go beyond the spirit covered by the description and the drawings, should fall within the protection scope of the present disclosure.