Electrodeposition methods of gallium and gallium alloy films and related photovoltaic structures

Abstract

Photovoltaic devices and methods for preparing a p-type semiconductor layer for the photovoltaic devices generally include electroplating a layer of gallium or a gallium alloy onto a conductive layer by contacting the conductive layer with a plating bath free of complexing agents including a gallium salt, methane sulfonic acid or sodium sulfate and an organic additive comprising at least one nitrogen atom and/or at least one sulfur atom, and a solvent; adjusting a pH of the solution to be less than 2.6 or greater than 12.6. The photovoltaic device includes an impurity in the p-type semiconductor layer selected from the group consisting of arsenic, antimony, bismuth, and mixtures thereof. Various photovoltaic precursor layers for forming CIS, CGS and CIGS p-type semiconductor structures can be formed by electroplating the gallium or gallium alloys in this manner. Also disclosed are processes for forming a thermal interface of gallium or a gallium alloy with the electroplating process.

1 . A method of forming a p-type semiconductor layer for a photovoltaic device, comprising:
 electroplating a first layer onto a conductive surface of a substrate, wherein said first layer is selected from the group consisting of a copper layer and a copper-gallium layer;   electroplating a second layer onto said first layer, wherein said second layer is selected from the group consisting of an indium layer, a gallium layer, an indium-gallium layer, a copper-indium diselenide layer, and a copper-gallium-diselenide layer; and optionally   electroplating a third layer onto said second layer, wherein said third layer is selected from the group consisting of a gallium layer and an indium layer; and   optionally electroplating a fourth layer onto said third layer, wherein said fourth is selected from the group consisting of selenium and sulfur; wherein said electroplating is carried out by a method comprising: contacting: (i) a substrate and (ii) a solution comprising: a precursor comprising an element selected from the group consisting of copper, gallium, indium, selenium, sulfur and a combination thereof; optionally a metalloid compound additive; further optionally an organic additive having at least a sulfur atom; and a solvent to dissolve said precursors; wherein the solution is free of complexing agents; adjusting a pH of said solution to a range selected from the group consisting of a pH of about zero to less than about 2.6 and a pH of about 12.6 to about 14, and applying a current to electroplate said substrate to produce said first, second, third or fourth layers; and   annealing said first, said second and said third layers in the presence of a selenium source and/or sulfur source to form the p-type semiconductor layer.   
     
     
         2 . The method of  claim 1 , wherein the conductive surface is selected from the group consisting of molybdenum, tantalum, tungsten, titanium, and corresponding nitrides thereof. 
     
     
         3 . The method of  claim 1 , wherein the plating bath comprises sodium sulfate at a concentration of 0.01 M to 2 M. 
     
     
         4 . The method of  claim 1 , wherein the plating bath further comprises an oxide of a metalloid. 
     
     
         5 . The method of  claim 4 , wherein the oxide of the metalloid is in an amount of 1 part per million to 10,000 parts per million. 
     
     
         6 . The method of  claim 1 , wherein the organic additive is selected from the group consisting of thioureas, thiazines, sulfonic acids, sulfonic acids, allyl phenyl sulfone, sulfamides, dithioxo-bishydroxylaminomolybdenum complex, and derivatives thereof. 
     
     
         7 . The method of  claim 1 , wherein the solution comprises an alkane sulfonic acid selected from the group consisting of methane sulfonic acid, ethane sulfonic acid, propane sulfonic acid, and butane sulfonic acid, and wherein the alkane sulfonic acid is at a concentration of 0.1 M to 2 M. 
     
     
         8 . The method of  claim 1 , wherein the p-type semiconductor has a ratio of Cu/(In+Ga) at 0.8 to 0.9 and a ratio of Ga/(Ga+In) at 0.3 to 0.33. 
     
     
         9 . A photovoltaic device comprising:
 at least one layer comprising gallium or indium or alloys comprising gallium and indium, wherein the at least one layer is formed by electrodeposition; and   an impurity in the at least one layer selected from the group consisting of arsenic, antimony, bismuth, selenium, sulfur and mixtures thereof.   
     
     
         10 . The photovoltaic device of  claim 9 , wherein the at least one layer forms a copper-gallium-indium-selenium layer. 
     
     
         11 . The photovoltaic device of  claim 9 , wherein the at least one layer forms a copper-indium-selenium layer. 
     
     
         12 . The photovoltaic device of  claim 9 , wherein the at least one layer forms a copper-gallium-selenium layer. 
     
     
         13 . The photovoltaic device of  claim 10 , wherein a ratio of Cu/(In+Ga) is at 0.8 to 0.9 and a ratio of Ga/(Ga+In) is at 0.3 to 0.33. 
     
     
         14 . A method for forming a thermal interface, the method comprising:
 electroplating a layer of gallium or a gallium alloy onto a heat emitting surface coupled to a microprocessor, wherein electroplating the gallium or gallium alloy comprises contacting the heat emitting surface with a plating bath free of complexing agents comprising a gallium salt and an optional organic additive comprising at least one sulfur atom, and a solvent; adjusting a pH of the plating bath to a range selected from the group of a pH of greater than about zero to less than 2.6 and a pH greater than about 12.6 to about 14, and applying a current to electroplate the heat emitting surface to produce a layer of the gallium or gallium alloy; and   coupling a heat sink or a heat spreader to the layer of gallium or the gallium alloy to form the thermal interface.   
     
     
         15 . The method of  claim 14 , wherein the plating bath comprises an alkane sulfonic acid selected from the group consisting of methane sulfonic acid, ethane sulfonic acid, propane sulfonic acid, and butane sulfonic acid, and wherein the alkane sulfonic acid is at a concentration of 0.1 M to 2 M. 
     
     
         16 . The method of  claim 14 , wherein the solution comprises sodium sulfate at a concentration of 0.01 M to 2 M. 
     
     
         17 . The method of  claim 14 , wherein the organic additive is selected from the group consisting of thioureas, thiazines, sulfonic acids, sulfonic acids, allyl phenyl sulfone, sulfamides, dithioxo-bishydroxylaminomolybdenum complex, and derivatives thereof.