Roll-To-Roll Electroplating for Photovoltaic Film Manufacturing

Abstract

A roll to roll system for forming an absorber structure for solar cells on a flexible foil as the flexible foil is advanced through units of the system and by unwrapping from a supply spool and wrapping around a take-up spool. Surface of the flexible foil is first conditioned in a conditioning unit to form an activated surface. A precursor stack including copper, gallium and indium layers is electroplated onto the activated surface by utilizing separate electroplating units for each layers. The precursor layer is reacted with at least one of Se and S in an annealing unit of the system.

1 . A system for forming an absorber structure for solar cells on a front surface of a continuous flexible workpiece as the continuous flexible workpiece is advanced through units of the system, comprising: 
 a conditioning unit to condition the front surface of the continuous flexible workpiece to form activated surface portions, wherein the activated surface portions present a consistently active surface substantially along the continuous flexible workpiece for electroplating;    a first electroplating unit to form a first layer of a precursor stack by electroplating a metal belonging to one of Group IB and Group IIIA over one of the activated surface portions of the continuous flexible workpiece as the continuous flexible workpiece is advanced through the first electroplating station;    a first cleaning unit to clean the first layer deposited in the first electroplating unit;    a second electroplating unit to form a second layer of the precursor stack by electroplating another metal belonging to the other of the Group IB and Group IIIA over the first layer as the continuous flexible workpiece is advanced through the second electroplating units and while the first layer is continued to be electroplated onto a following one of the activated surface portions of the surface of the continuous flexible workpiece in the first electroplating unit, wherein the first layer is different from the second layer;    a second cleaning unit to clean the second layer deposited in the second electroplating unit; and    a moving assembly to hold and linearly move the continuous flexible workpiece through the units of the system, wherein the moving assembly comprises a feed spool to unwrap and feed unprocessed portions of the continuous flexible workpiece into the system and a take-up spool to receive processed portions and wrap them around.    
     
     
         2 . The system of  claim 1  further comprising a third electroplating unit to form a third layer by electroplating a further metal belonging to one of the Group IB and Group IIIA over the second layer to obtain the precursor stack as the continuous flexible foil is advanced through the first, second and third electroplating stations and while the second layer is continued to be electroplated in the second electroplating station on the first layer that is electroplated on the following activated portion of the surface of the continuous flexible workpiece, and while the first layer is continued to be electroplated onto a further following one of the activated surface portions of the surface of the continuous flexible workpiece in the first electroplating station, wherein the third layer is different from the first and second layers.  
     
     
         3 . The system of  claim 2  further comprising one of a cleaning-drying unit to clean and dry the third layer and a third cleaning unit to clean the third layer deposited in the third electrodeposition unit.  
     
     
         4 . The system of  claim 3  further comprising an annealing unit to react the first, second and third layers.  
     
     
         5 . The system of  claim 3  further comprising a fourth electrodeposition unit to deposit a fourth layer of a Group VIA material over the third layer.  
     
     
         6 . The system of  claim 5 , wherein the Group VI material includes one of Se, S and Te.  
     
     
         7 . The system of  claim 5  further comprising a cleaning-drying unit to clean and dry the fourth layer and an annealing unit to react the first, second, third and fourth layers.  
     
     
         8 . The system of  claim 1 , wherein the conditioning unit comprises at least one of: 
 an electrotreating chamber having an electrotreating solution and electrode that can be anodically or cathodically polarized with respect to the front surface of the continuous flexible workpiece to form the activated portions,    a deposition chamber to deposit a seed layer over the front surface of the continuous flexible workpiece a pickling chamber to treat the front surface of the continuous flexible workpiece to form the activated portions, and    an etching chamber to etch the front surface of the continuous flexible workpiece to form the activated portions.    
     
     
         9 . The system of  claim 1 , wherein the Group IB material includes Cu and wherein the first Group IIIA material includes one of Ga and In.  
     
     
         10 . The system of  claim 1  further comprising a packing supply spool to provide a continuous packing sheet to place onto the processed portions as the continuous flexible workpiece is wrapped around the take-up spool.  
     
     
         11 . The system of  claim 9  further comprising a deposition monitoring unit to monitor and control the thickness of deposited first, second and third layers.  
     
     
         12 . The system of  claim 11  wherein the deposition monitoring unit provides a feedback signals to each of the first, second and third electrodeposition units to cause the thicknesses of deposited first, second and third layers to converge toward a predetermined thickness for each of the first, second and third layers.  
     
     
         13 . The system of  claim 12  wherein the convergence is to maintain target ratios of Cu/In+Ga and Ga/In+Ga.  
     
     
         14 . A process of forming a precursor stack on a frontside of a continuous flexible workpiece using a system including a moving assembly, wherein the frontside includes a conductive layer, comprising: 
 moving the continuous flexible workpiece into and sequentially through a conditioning unit, an activated surface cleaning unit, a first electroplating unit, a first cleaning unit, a second electroplating unit, a second cleaning unit, a third electroplating unit, and a cleaning-drying unit by feeding previously unrolled portions of the continuous flexible workpiece from an input end of the system;    conditioning the surface of the conductive layer in the conditioning unit to form an activated surface portion, wherein the activated surface portion presents a consistently uniform surface along substantially an entirety of the continuous flexible workpiece for electroplating;    cleaning the activated surface portion in the activated surface cleaning unit;    forming a precursor stack over the activated surface portion after cleaning the activated surface portion, comprising: 
 forming a first material layer over the activated surface portion by electrodepositing one of a Group IB material and a Group IIIA material in the first electroplating unit;  
 cleaning the first material layer in the first cleaning unit;  
 forming a second material layer over the first material layer by electrodepositing the other of the Group IB material and the Group IIIA material in the second electroplating unit, wherein the second material layer is different from the first material layer;  
 cleaning the second material layer in the second cleaning unit;  
 forming a third material layer over the second material layer by depositing another of the Group IB material and the Group IIIA material in the third electroplating unit, wherein the third material layer is different from the first and the second material layers; and  
 cleaning and drying the precursor stack in the cleaning-drying unit; and  
 taking up and wrapping processed portion of the continuous flexible workpiece at an output end of the system.  
   
     
     
         15 . The process of  claim 14  further comprising: 
 cleaning the precursor stack in a third cleaning unit prior to cleaning and drying; and    forming a fourth material layer over the precursor stack by depositing at least one Group VIA material from a fourth deposition unit; and wherein the moving the continuous flexible workpiece into and sequentially through includes the third cleaning unit and the fourth deposition unit.    
     
     
         16 . The process of  claim 15  further comprising reacting the precursor stack and the fourth layer in an annealing unit; and wherein the moving the continuous flexible workpiece into and sequentially through includes the annealing unit.  
     
     
         17 . The process of  claim 16 , wherein the at least one Group VI material comprises one of Se, S and Te.  
     
     
         18 . The process of  claim 15 , wherein the at least one Group VI material comprises one of Se, S and Te.  
     
     
         19 . The process of  claim 15 , wherein the at least one Group VIA material is deposited by one of dipping the precursor stack into an ink solution including nano-particles of the at least one Group VIA material and depositing by electrodeposition the at least one Group VIA material onto the precursor stack.  
     
     
         20 . The process of  claim 14  further comprising reacting the precursor stack in an annealing unit with at least one Group VIA material after cleaning and drying; and wherein the moving the continuous flexible workpiece into and sequentially through includes the annealing unit.  
     
     
         21 . The process of  claim 14  wherein conditioning comprises one of electrotreating the conductive layer in a process solution with respect to an electrode by applying one of cathodic and anodic polarization deposit a seed layer onto the front surface of the continuous flexible workpiece and pickling the front surface of the continuous flexible workpiece to form the activated portion.  
     
     
         22 . The process  claim 14  wherein the conditioning comprises depositing a seed layer on the contact layer.  
     
     
         23 . The process of  claim 14 , wherein the Group IB material includes Cu and wherein the Group IIIA material includes one of Ga and In.  
     
     
         24 . The process of  claim 14  further comprising, forming a fifth material layer after forming the second layer, wherein the fifth layer and the first layer are the same, and forming a sixth layer after forming the third layer, wherein the sixth and the second layer are the same.