Method of preparing solar cell front contacts

Abstract

Method of preparing on a solar cell the top contact pattern which consists of a set of parallel narrow finger lines and wide collector lines deposited essentially at right angles to the finger lines on the semiconductor substrate, characterized in that it comprises at least the following steps: (a) screen printing and drying the set of contact finger lines; (b) printing and drying the wide collector lines on the top of the set of finger lines in a subsequent step; (c) firing both finger lines and collector lines in a single final step in order to form an ohmic contact between the finger lines and the semiconductor substrate and between the finger lines and the wide collector lines.

We claim:  
     
       1. A method of preparing a contact pattern on a semiconductor substrate of a solar cell, said patterning comprising a set of narrow finger lines and wide collector lines that intersect and that are in electrical contact, said method comprising the steps of: 
       (1) screen printing a masking paste on top of a front surface of said semiconductor substrate using a screen with a pattern structure, thereby forming a printed pattern;  
       (2) depositing a coating over said front surface;  
       (3) dissolving said masking paste whereby selectively lifting-off the part of the coating deposited on top of the masking paste; and thereafter  
       (4) etching off oxide layers from areas of said front surface exposed through openings in the coating, wherein said openings are formed through the dissolving and lift-off step (3); and thereafter  
       (5)  screen printing the set of finger lines in said  openings formed in said coating using a screen with said pattern structure and drying the set of finger lines.  
     
     
       2. The method of  claim 1 , wherein the step of depositing a coating over the front surface comprises depositing an antireflection layer. 
     
     
       3. The method of  claim 1  further comprising the steps of: 
       printing and drying the collector lines on top of the set of finger lines; and  
       firing both the finger lines and the collector lines.  
     
     
       4. The method of  claim 1  further comprising the steps of: 
       subsequently, printing and drying the collector lines on top of the set of finger lines; and  
       firing both the finger lines and the collector lines in a single final step.  
     
     
       5. The method of  claim 4 , wherein substrates  a substrate already having a rear ohmic contact are  is used. 
     
     
       6. The method of  claim 4 , wherein said step of screen printing the set of finger lines comprises the use of a screen made of a solid metal mask. 
     
     
       7. The method of  claim 6 , wherein the set of finger lines and the collector lines are made with silver paste. 
     
     
       8. The method of  claim 4 , wherein the collector lines are printed by a process selected from the group consisting of screen printing, ink-jet printing, and off-set printing. 
     
     
       9. The method of  claim 8  wherein the set of finger lines and the collector lines are made with silver paste. 
     
     
       10. The method as recited in  claim 1  further comprising the steps of: 
       forming an oxide layer on top of said substrate thereby forming said front surface;  
       thereafter executing steps (1) to (3),  
       etching of said oxide layer through openings in the coating;  
       and thereafter executing step (4)  etching off oxide layers from areas of said front surface exposed through openings in the coating, wherein said openings are formed through the dissolving and lift- off step  (   3   ).  
     
     
       11. The method of  claim 1 , wherein said masking paste comprises metal powders or powders of silicon oxide or powders of titanium oxide or chalk powder, mixed with an organic material. 
     
     
       12. The method of  claim 1  wherein the step of dissolving the masking paste is executed by immersing said substrate in an organic solvent. 
     
     
       13. The method of  claim 1 , wherein the step of dissolving the masking paste is executed by immersing said substrate in a solution of sulfuric acid and hydrogen peroxide.