Photovoltaic cell with porous semiconductor regions for anchoring contact terminals, electrolitic and etching modules, and related production line

Abstract

A photovoltaic cell ( 100 ) is proposed. The photovoltaic cell includes a substrate ( 105; 105 ′) of semiconductor material, and a plurality of contact terminals (Tf,Tb) each one arranged on a corresponding contact area ( 122 ) of the substrate for collecting electric charges being generated in the substrate by the light. For at least one of the contact areas, the substrate includes at least one porous semiconductor region ( 125 ) extending from the contact area into the substrate for anchoring the whole corresponding contact terminal on the substrate. In the solution according to an embodiment of the invention, each porous semiconductor region has a porosity decreasing moving away from the contact area inwards the substrate. An etching module ( 400 ) and an electrolytic module ( 700;700′;800;800 ′) for processing photovoltaic cells, a production line ( 900 ) for producing photovoltaic cells, and a process for producing photovoltaic cells are also proposed.

1 . An electrolytic module for performing an electrolytic process on a substrate the electrolytic module including a set of processing heads each one including:
 a support element having an operative surface,   at least one delivery mouth for delivering a solution on the operative surface, the support element being made at least partially of an electrically conductive material for contacting the solution,   at least one suction mouth arranged around said at least one delivery month on the operative surface for sucking the delivered solution thereby forming a dynamic meniscus on the operative surface when in contact with a corresponding portion of the substrate;   
       one of the processing heads being an electrolytic head for providing a dynamic meniscus of an electrolytic solution, 
       wherein the electrolytic module further includes:
 first biasing means for applying a first biasing voltage to the electrolytic solution through the electrolytic head, and 
 second biasing means for applying a second biasing voltage to the substrate. 
 
     
     
         2 . The electrolytic module according to  claim 1 , wherein the support element of each processing head is made of a semiconductor material or of a polymeric material with a contact terminal for electrically contacting the solution. 
     
     
         3 . The electrolytic module according to  claim 1 , wherein the electrolytic head acts on a first surface of the substrate the second biasing means including means for applying the second biasing voltage to a second surface of the substrate opposite the first surface of the substrate to create a conductive path with the electrolytic head through the substrate. 
     
     
         4 . The electrolytic module according to  claim 1 , wherein the electrolytic head acts on a first surface of the substrate the second biasing means including at least one biasing head of the processing heads each one for providing a dynamic meniscus of a conductive solution, and means for applying the second biasing voltage to the conductive solution through each biasing head, said at least one biasing head acting on the first surface of the substrate to create a conductive path with the electrolytic head through the substrate. 
     
     
         5 . The electrolytic module according to  claim 4 , further including moving means for moving the substrate and the electrolytic module with respect to each other along a movement direction, said at least one biasing head including a first biasing head and a second biasing head arranged upstream and downstream, respectively, the electrolytic head along the movement direction for maintaining the conductive path while the substrate passes through the electrolytic module. 
     
     
         6 . The electrolytic module according to  claim 1 , further including means for controlling a size of the dynamic meniscus by changing an inflow of the solution and/or a depression in each suction mouth. 
     
     
         7 . The electrolytic module according to  claim 1 , wherein the electrolytic module is an anodization module for performing an anodization process on the substrate. 
     
     
         8 . The electrolytic module according to  claim 7 , wherein the anodization module includes means for forming porous semiconductor regions on the substrate. 
     
     
         9 . The electrolytic module according to  claim 1 , wherein the electrolytic module is a deposition module for electrolytically depositing conductive structures (Tf,Tb) on the substrate. 
     
     
         10 . The electrolytic module according to  claim 9 , wherein the deposition module further includes means for moving away the substrate and the electrolytic head along a deposition direction of the conductive structures (Tf,Tb) transversally to the substrate during the deposition thereof to obtain an elongated shape of the conductive structures along the deposition direction. 
     
     
         11 . The electrolytic module according to  claim 10 , wherein the deposition module further includes means for moving the substrate and the electrolytic head along a shifting direction transversally to the deposition direction during the deposition of the conductive structures (Tf,Tb) to obtain a variable section of the conductive structures along the deposition direction. 
     
     
         12 . The electrolytic module according to  claim 11 , wherein the means for moving the substrate and the electrolytic head ( 801   b ) along the shifting direction includes means for rotating the substrate with respect to the electrolytic head during the deposition of the conductive structures (Tf,Tb). 
     
     
         13 . The electrolytic module according to  claim 9 , wherein the deposition module includes at least one further suction mouth arranged inside each delivery month on the operative surface for sucking the delivered solution thereby forming an empty region inside the corresponding dynamic meniscus to generate a hollow structure of the conductive structures (Tf,Tb). 
     
     
         14 . An etching module for performing an etching process on a substrate the etching module including an etching head including:
 a support element having an operative surface,
 at least one delivery mouth for delivering an etching solution on the operative surface, and 
   at least one suction mouth completely surrounding said at least one delivery month on the operative surface for sucking the delivered etching solution thereby forming a dynamic meniscus on the operative surface when in contact with a corresponding portion of the substrate.   
     
     
         15 . The etching module according to  claim 14 , further including means for controlling a size of the dynamic meniscus by changing an inflow of the solution and/or a depression in each suction mouth. 
     
     
         16 . (canceled) 
     
     
         17 . The production line according to  claim 16 , further including means for feeding each substrate across the etching station, the anodization station and/or the deposition station along a feeding direction. 
     
     
         18 . The production line according to  claim 17 , wherein
 the etching station includes, for each one of a plurality of strips of the contact area, an etching module for forming the corresponding strip of the contact area when the substrate passes through the etching station, and/or   the anodization station includes, for each one of a plurality of strips of the porous semiconductor region an anodization module for forming the corresponding strip of the porous semiconductor region when the substrate passes through the anodization station, and/or   the deposition station includes, for each one of a plurality of strips of the contact terminal (Tf,Tb), a deposition module for forming the corresponding strip of the contact terminal when the substrate passes through the deposition station.   
     
     
         19 . The production line according to  claim 17 , wherein
 the anodization station includes a single anodization module extending transversally to the feeding direction for forming a plurality of strips of the contact area when the substrate passes through the anodization station, and/or   the deposition station includes a single deposition module extending transversally to the feeding direction for forming a plurality of strips of the contact terminal when the substrate passes through the deposition station.   
     
     
         20 . The production line according to  claim 18 , wherein each electrolytic head of the etching station, the anodization station and/or the deposition station is shorter than the substrate along the feeding direction. 
     
     
         21 . The production line according to  claim 18 , further including:
 means for first rotating the substrate exiting the etching station by a first rotation angle equal to 90°, and a further etching station for forming a set of further strips of the contact area extending perpendicularly to said strips of the contact area when the first rotated substrate passes through the further etching station, and/or   means for second rotating the substrate exiting the anodization station by a second rotation angle equal to 90°, and a further anodization station for forming a set of further strips of the semiconductor porous region extending perpendicularly to said strips of the semiconductor porous region when the second rotated substrate passes through the further anodization station, and/or   means for third rotating the substrate exiting the deposition station by a third rotation angle equal to 90°, and a further deposition station for forming a set of further strips of the contact terminal (Tf) extending perpendicularly to said strips of the contact terminal when the third rotated substrate passes through the further deposition station.   
     
     
         22 . The production line according to  claim 18 , further including:
 means for fourth rotating the substrate exiting the etching station by a fourth rotation angle higher than 0° and lower than 90° to cause the anodization station to form the semiconductor porous region when the fourth rotated substrate passes through the anodization station, and/or   means for fifth rotating the substrate exiting the anodization station by a fifth rotation angle higher than 0° and lower than 90° to cause the deposition station to form the contact terminal (Tf) when the fifth rotated substrate passes through the deposition station.   
     
     
         23 . The production line according to  claim 22 , wherein said fourth rotating angle and said fifth rotating angle are equal to 45°. 
     
     
         24 . The production line according to  claim 17 , wherein
 the etching station includes a single etching module for forming the contact area when the substrate is stopped in the etching station and coupled therewith, and/or   the anodization station includes a single anodization module for forming the semiconductor porous region when the substrate is stopped in the anodization station and coupled therewith, and/or   the deposition station includes a single deposition module for forming the contact terminal (Tf) when the substrate is stopped in the deposition station and coupled therewith.   
     
     
         25 . A photovoltaic cell including a substrate of semiconductor material, a plurality of contact terminals (Tf,Tb) each one arranged on a corresponding contact area of the substrate for collecting electric charges being generated in the substrate by the light, for at least one of the contact areas the substrate including at least one porous semiconductor region extending from the contact area into the substrate for anchoring the whole corresponding contact terminal on the substrate: wherein each porous semiconductor region has a porosity decreasing moving away from the contact area inwards the substrate. 
     
     
         26 . The photovoltaic cell according to  claim 25 , wherein each porous semiconductor region has a thickness lower than 1 μm, the corresponding contact terminal (Tf,Tb) being penetrated inside the whole thickness of the region of porous semiconductor region. 
     
     
         27 . The photovoltaic cell according to  claim 25 , wherein each porous semiconductor region includes an external layer proximate to the corresponding contact area with decreasing porosity and an internal layer distal from the contact area with uniform porosity. 
     
     
         28 . The photovoltaic cell according to  claim 27 , wherein the porosity of the external layer decreases from a maximum value to a minimum value, and wherein the porosity of the internal layer is comprised between said maximum value and said minimum value. 
     
     
         29 . The photovoltaic cell according to  claim 27 , wherein the internal layer is thicker than the external layer. 
     
     
         30 . The photovoltaic cell according to  claim 25 , wherein said at least one porous semiconductor region of each contact area has a porosity decreasing moving inwards the contact area from a border thereof. 
     
     
         31 . The photovoltaic cell according to  claim 30 , wherein said at least one porous semiconductor region each contact area includes a plurality of porous semiconductor regions decreasing in concentration and/or size moving inwards the contact area from the border thereof. 
     
     
         32 . A process for producing a photovoltaic cell, the process including the steps of:
 providing a substrate of semiconductor material having a front surface for absorbing the light,   forming at least one front contact terminal (Tf) arranged on a front contact area of the front surface for collecting electric charges being generated in the substrate by the light,   wherein the front contact area and the front contact terminal have a flat profile, the step of forming at least one front contact terminal including:   forming at least one front porous semiconductor region extending from the front contact area into the substrate for anchoring the whole front contact terminal on the substrate, and   chemically depositing the front contact terminal.   
     
     
         33 . The process according to  claim 32 , wherein the step of forming at least one front contact terminal is performed at a temperature lower than 350° C. 
     
     
         34 . The process according to  claim 32 , wherein the step of forming at least one front porous semiconductor region includes:
 subjecting a front layer of the substrate corresponding to the porous semiconductor region to an anodic process in a dark condition, the front layer being silicon of the N-type with a doping concentration lower than 1·10 17  atoms/cm 3 .   
     
     
         35 . The process according to  claim 34 , the dark condition is lower then 2 lux.