Reel-to-reel plating of conductive grids for flexible thin film solar cells

Abstract

The present inventions provide structures and methods for manufacturing high electrical conductivity grid patterns having minimum shadowing effect on the illuminated side of the solar cells. In a particular aspect, a width of an effective channel region is greater than a spacing that exists between conductive elements in adjacent grid patterns that exist along a lengthwise direction of a continuous workpiece.

1 . A method of roll to roll manufacturing low electrical resistivity conductive grids having reduced shading effect for solar cells, comprising:
 providing a flexible continuous workpiece, the flexible continuous workpiece comprising a continuous flexible substrate, a bottom contact layer disposed atop the continuous flexible substrate, an absorber layer disposed atop the bottom contact layer, a transparent conductive layer disposed atop the absorber layer, and a first conductive film having a first resistivity disposed atop predetermined areas of a top surface of the transparent conductive layer and in electrical communication with the transparent conductive layer to form a raised grid pattern along a length of the flexible continuous workpiece, wherein the raised grid pattern includes a plurality of adjacent grids, with each grid having a predetermined grid width, a predetermined grid length, and a predetermined spacing between adjacent grids along the length direction of the flexible continuous workpiece, wherein a sheet resistance of the first conductive film is less than the sheet resistance of the transparent conductive layer, and wherein the top surface of the transparent conductive layer and the raised grid pattern disposed thereon form a front surface of the flexible continuous workpiece;   applying an electrodeposition solution onto an effective plating region established on a portion of the front surface, including a part of the first conductive film, and onto an anode placed across from the portion of the front surface, the effective plating region having a length that is substantially the same as a width of the workpiece and a predetermined width that is at least longer than the predetermined spacing between adjacent grids;   applying a voltage between the anode and the part of the first conductive film;   selectively electrodepositing a conductive material from the electrodeposition solution onto the first conductive film and not the transparent conductive layer to form a second conductive film having a second resistivity atop the first conductive film, thereby forming the low electrical resistivity conductive grids having reduced shading effect, wherein the first resistivity is greater than the second resistivity; and   moving the front surface, including the part of the first conductive film, through the effective plating region, during the steps of applying the electrodeposition solution, applying the voltage, and selectively electrodepositing.   
     
     
         2 . The method of  claim 1 , wherein each grid includes fingers disposed parallel to the flexible continuous workpiece edges extending along the length of the flexible continuous workpiece. 
     
     
         3 . The method of  claim 2 , wherein in the step of moving, portions of the flexible continuous workpiece are continuously advanced into a front side of the effective plating region and through the effective plating region to form the second conductive film and then continuously advanced out of the effective plating region through a back side of the effective plating region after forming the second conductive film. 
     
     
         4 . The method of  claim 3  wherein the step of selectively electrodepositing includes applying a first electrical contact adjacent the front side of the effective plating region and a second electrical contact adjacent the back side of the effective plating region, wherein a distance between the first and second contacts is less than or equal to the length of each of the fingers. 
     
     
         5 . The method of  claim 4 , wherein in the step of moving the portions of the flexible continuous workpiece are released from a supply roll of the flexible continuous workpiece and wound as a receiving roll when advanced out of the -effective plating region. 
     
     
         6 . The method of  claim 4 , wherein the first and the second contacts are conductive roll contacts rolling on the front surface as the flexible continuous workpiece is advanced. 
     
     
         7 . The method of  claim 4 , wherein the first and the second contacts are conductive brush contacts sweeping the front surface as the flexible continuous workpiece is advanced. 
     
     
         8 . The method of  claim 1 , wherein the first resistivity of the first conductive film is in the range of 10-30 micro ohm-cm, the second resistivity of the second conductor is in the range of 2-10 micro ohm-cm, and the resistivity of the transparent conductive layer is in the range of 200-500 micro ohm-cm. 
     
     
         9 . The method of  claim 1 , wherein the first conductive film includes a silver (Ag) based conductive material formed using one of a screen printing process and an ink jet printing process. 
     
     
         10 . The method of  claim 1 , wherein the second conductive film includes one of copper, silver, a copper alloy and a silver alloy. 
     
     
         11 . The method of  claim 1 , wherein the transparent conductive layer includes a stack including a transparent buffer layer deposited over the absorber layer and a transparent conductive oxide (TCO) layer deposited over the transparent buffer layer, and wherein the transparent buffer layer includes one of CdS and ZnS, and the TCO layer includes one of ZnO and indium tin oxide (ITO). 
     
     
         12 . The method of  claim 1 , wherein the absorber layer includes a group IBIIIAVIA compound semiconductor. 
     
     
         13 . The method of  claim 1 , wherein the substrate includes one of a stainless steel foil and an aluminum foil. 
     
     
         14 . The method of  claim 1 , wherein the bottom contact layer includes at least one of Mo, W, Ta, Ti, Cr and Ru materials. 
     
     
         15 . The method of  claim 1 , wherein the effective plating region is defined by an enclosure including a front wall and a back wall extending along the length of the effective plating region and two side walls extending along the width of the effective plating region. 
     
     
         16 . The method of  claim 15 , wherein the flexible continuous workpiece enters the effective plating region through an entrance opening the in the front wall and exits the effective plating region through an exit opening in the back wall. 
     
     
         17 . The method of  claim 16 , wherein the electrodeposition solution is delivered through a top opening of the enclosure and used electrodeposition solution flows out of the enclosure through at least one of the entrance and exit openings. 
     
     
         18 . The method of  claim 5 , wherein the effective plating region is defined by an enclosure including a front wall and a back wall extending along the length of the effective plating region and two side walls extending along the width of the effective plating region, wherein the front and the back walls forms the front and back sides of the effective plating region, respectively. 
     
     
         19 . The method of  claim 18 , wherein the electrodeposition solution is delivered through a top opening of the enclosure and used electrodeposition solution flows out of the enclosure through at least one of the entrance and exit openings. 
     
     
         20 . The method of  claim 19 , wherein the first and the second contacts are conductive roll contacts rolling on the front surface as the flexible continuous workpiece is advanced. 
     
     
         21 . The method of  claim 19 , wherein the first and the second contacts are conductive brush contacts sweeping the front surface as the flexible continuous workpiece is advanced. 
     
     
         22 . The method of  claim 1 , wherein the thickness of the first conductive film is in the range of 1-10 microns. 
     
     
         23 . The method of  claim 1 , wherein the thickness of the second conductive film is in the range of 1-5 microns. 
     
     
         24 . The method of  claim 1 , wherein the thickness of the transparent conductive layer is in the range of 0.1-0.5 microns.