Chalcogenide-based materials and improved methods of making such materials

Abstract

The present invention provides strategies for making high quality CIGS photoabsorbing materials from precursor films that incorporate a sub-stoichiometric amount of chalcogen(s). Chalcogen(s) are incorporated into the CIGS precursor film via co-sputtering with one or more other constituents of the precursor. Optional annealing also may be practiced to convert precursor into more desirable chalcopyrite crystalline form in event all or a portion of the precursor has another constitution. The resultant precursors generally are sub-stoichiometric with respect to chalcogen and have very poor electronic characteristics. The conversion of these precursors into CIGS photoabsorbing material via chalcogenizing treatment occurs with dramatically reduced interfacial void content. The resultant CIGS material displays excellent adhesion to other layers in the resultant photovoltaic devices. Ga migration also is dramatically reduced, and the resultant films have optimized Ga profiles in the top or bottom portion of the film that improve the quality of photovoltaic devices made using the films.

What is claimed is: 
     
         1 . A photovoltaic device comprising a chalcogen-containing photoabsorbing film made by a process comprising the steps of:
 (a) sputtering at least one target in the presence of one or more chalcogens comprising Se to form a Se-containing precursor of the chalcogen-containing photoabsorber wherein the Se-containing precursor includes a sub-stoichiometric amount of the one or more chalcogens comprising Se throughout the precursor or in selected areas of the precursor; and   (b) while the precursor comprises Se throughout the precursor or in the selected areas of the precursor, subjecting the Se-containing precursor to a thermal treatment in the presence of one or more chalcogens comprising Se that selenizes the precursor to form the selenium-containing photoabsorbing composition.   
     
     
         2 . A photovoltaic device, comprising a chalcogen-containing photoabsorbing film having a top surface and a bottom surface, said photoabsorbing film comprising:
 a void content of 0.5 to 50%; and   0.1 to 60 atomic percent Ga at least in a first boundary region proximal to the bottom surface of the photoabsorbing film and/or a second boundary region proximal  t o the top surface of the photoabsorbing film, wherein the atomic percent Ga is based on  t h e  total composition of the corresponding boundary region.   
     
     
         3 . The photovoltaic device of  claim 2 , wherein the Ga is included in the first and second boundary regions and wherein at least one additional region is interposed between the first and second boundary regions, wherein the additional region includes a reduced Ga content relative to the first and second boundary regions. 
     
     
         4 . The photovoltaic device of  claim 2 , wherein the photoabsorbing film incorporates ingredients comprising Cu, In, Ga, and Se. 
     
     
         5 . The photovoltaic device of  claim 2 , wherein at least one of the first and/or second boundary regions has a thickness in the range from about 10 nm to about 300 nm and the at least one boundary region comprises from about 2 to about 10 atomic percent Ga based on the total composition of the at least one boundary region. 
     
     
         6 . The photovoltaic device of  claim 2 , further comprising an electrical contact region on the bottom surface of the chalcogen-containing photoabsorbing film and having an interface therebetween. 
     
     
         7 . The photovoltaic device of  claim 2 , wherein at least more than 10% of the total void area includes voids that contact inner surfaces of the photoabsorbing film only and do not contact the interface between the chalcogen-containing photoabsorbing film and the electrical contact region. 
     
     
         8 . The photovoltaic device of  claim 2 , wherein at least one chalcogen is incorporated into at least one of the first and second boundary regions. 
     
     
         9 . The photovoltaic device of  claim 2 , wherein at least one chalcogen is incorporated into each of the first and second boundary regions. 
     
     
         10 . The photovoltaic device of  claim 9 , wherein the chalcogen is Se. 
     
     
         11 . The photovoltaic device of  claim 2 , wherein the void content comprises voids having an average size of from 0.1 microns to 2 microns. 
     
     
         12 . A precursor film of a chalcogen-containing photoabsorbing material, said precursor comprising from about 0.1 to about 60 atomic percent Ga selectively co-incorporated into one or more portions of the precursor with at least one chalcogen based upon the total composition of said portion; and wherein the precursor includes a sub-stoichiometric amount of a chalcogen based upon the overall composition of the precursor film. 
     
     
         13 . The photovoltaic device of  claim 12 , wherein the precursor film is at least partially amorphous. 
     
     
         14 . The photovoltaic device of  claim 12 , wherein the chalcogen comprises Se. 
     
     
         15 . The precursor film of  claim 12 , wherein the precursor comprises at least two metals selected from Cu, In, and Ga, and the atomic ratio of chalcogen to the cumulative amount of metals in the precursor is in the range from about 0.01 to 0.8. 
     
     
         16 . The precursor film of  claim 12 , wherein the precursor film has a top and a bottom, and wherein the precursor comprises a first region proximal to the bottom, a second region proximal to the top, and at least one region interposed between the first and second regions, wherein at least one chalcogen comprising Se is selectively incorporated into at least one of the first and second regions and is not included in at least one of the interposed regions. 
     
     
         17 . The precursor film of  claim 16 , wherein Ga is selectively co-incorporated into at least one of the regions that also include at least one chalcogen comprising Se.