Plating process

Abstract

Methods of plating electrical contacts on a photosensitive device are provided. Also provided are methods of plating electrical contacts on solar cells.

1 . A method of plating an electrical contact on a light-sensitive device displaying a photovoltaic effect, comprising providing a semiconductive wafer having at least two major surfaces, the wafer having a photovoltaic junction formed therein so that when one of the major surfaces of the wafer is exposed to light, negative charges collect at a first of the major surfaces and positive charges collect at a second of the major surfaces, contacting the wafer with a cyanide-free metal plating bath, applying a potential to the plating bath and exposing the wafer to light to deposit a layer of metal onto the first major surface, wherein the plating bath is an aqueous solution and comprises metal ions, at least one water-soluble nitro-containing compound, at least one surfactant, at least one amido-compound, and at least one component chosen from a water-soluble amino acid, a water-soluble sulfonic acid, and mixtures thereof. 
     
     
         2 . The method of  claim 1  further comprising the step of contacting the wafer with a solution comprising a sulfonic acid before contacting the wafer with the bath of cyanide-free silver electrolyte. 
     
     
         3 . The method of  claim 2  wherein the sulfonic acid is methane sulfonic acid. 
     
     
         4 . The method of  claim 1  wherein the light is continuous or pulsed. 
     
     
         5 . The method of  claim 1  wherein the wafer has an antireflective coating overlying the first major surface. 
     
     
         6 . The method of  claim 5  wherein the antireflective coating comprises one or more of a silicon oxide layer, a silicon nitride layer, and a combination of a silicon oxide layer and a silicon nitride layer. 
     
     
         7 . The method of  claim 1  wherein the bath further comprises a buffering agent and where the bath has a pH of 7 to 14. 
     
     
         8 . The method of  claim 1  wherein the metal is chosen from silver, gold and copper. 
     
     
         9 . The method of  claim 1  wherein the first major surface comprises a plurality of contacts. 
     
     
         10 . The method of  claim 1  further comprising providing a coating of the metal on the second major surface prior to contacting wafer with the cyanide-free metal plating bath. 
     
     
         11 . The method of  claim 1 , wherein the plating bath further comprises one or more vitamins.