Low-cost multi-junction solar cells and methods for their production

Abstract

Methods for fabricating solar cells without the need to perform gasification of metallurgical-grade silicon are disclosed. Consequently, the costs and health and environmental hazards involved in fabricating the solar or silicon grade silicon are being avoided. A solar cell structure comprises a metallurgical grade doped silicon substrate and a thin-film structure formed over the substrate to form a p-i-n junction with the substrate. The substrate may be doped p-type, and the thin film structure may be an intrinsic amorphous layer formed over the substrate and an n-type amorphous layer formed over the intrinsic layer.

1 . A method for producing a solar cell comprising:
 obtaining a multi-crystalline substrate consisting essentially of doped metallurgical grade silicon of purity of 99.9%-99.999% doped as one of a p-type or n-type and having an upper side and an underside, the upper side for facing the sun;   forming a first thin-film structure comprising an intrinsic silicon layer formed directly over and in direct contact with the upper side of the substrate and a first doped layer of opposite polarity as that of the substrate and formed directly over and in direct contact with the intrinsic layer, to thereby form a first p-i-n structure with the substrate;   forming a second thin-film structure over the first thin film structure;   forming a top conductive contact above the second thin-film structure;   forming a bottom conductive contact on the underside of the substrate.   
     
     
         2 . The method of  claim 1 , further comprising wet chemical etching the substrate so as to texture the substrate prior to forming a first thin-film structure. 
     
     
         3 . The method of  claim 1 , wherein forming a first thin-film structure comprises forming at least one of the first intrinsic layer and the first doped layer as an amorphous silicon layer. 
     
     
         4 . The method of  claim 3 , wherein in forming a first thin-film structure at least one of the first intrinsic layer and the first doped layer are formed to comprise hydrogen atoms dispersed within a silicon layer. 
     
     
         5 . The method of  claim 4 , wherein forming a bottom conductive contact comprises forming a doped conductive layer, of the same polarity as the substrate, on the underside of the substrate and forming a metal layer over the doped conductive layer. 
     
     
         6 . The method of  claim 5 , wherein forming the top conductive contact comprises forming a transparent conductor over the first doped layer. 
     
     
         7 . The method of  claim 6 , further comprising forming conductive electrodes over the transparent conductor. 
     
     
         8 . The method of  claim 5 , further comprising forming an amorphous intrinsic layer on the underside of the substrate such that it is positioned between the underside of the substrate and the doped conductive layer. 
     
     
         9 . The method of  claim 1 , wherein obtaining a multi-crystalline substrate comprises slowly solidifying metallurgical silicon melt into a cylinder with large silicon grains and resistivity of about 1 Ohmcm. 
     
     
         10 . The method of  claim 1 , wherein forming a the second thin-film structure comprises forming a first doped thin-film over the first thin-film structure, forming an intrinsic thin-film over the first doped thin-film, and forming a second doped thin-film over the intrinsic thin-film, to thereby form a second thin-film p-i-n structure over the first p-i-n structure. 
     
     
         11 . The method of  claim 1 , wherein the first doped layer is an n-type layer formed over and in contact with the intrinsic layer, and wherein forming the second thin-film structure comprises forming a p-type layer over and in contact with the first n-type layer, forming a second intrinsic layer over the p-type layer, and forming a second n-type layer. 
     
     
         12 . The method of  claim 11 , further comprising forming a diffusion layer in the metallurgical grade substrate, the diffusion layer being one of an n-type or p-type. 
     
     
         13 . The method of  claim 1 , wherein obtaining a multi-crystalline substrate comprises comprising obtaining silicon wafers consisting essentially of a p-type metallurgical grade silicon of resistivity of about 1.0 Ωcm. 
     
     
         14 . The method of  claim 1 , wherein obtaining a multi-crystalline substrate comprises fabricating multi-crystalline wafers doped with both boron and phosphorous and having p-type polarity. 
     
     
         15 . A method of fabricating a solar cell, comprising:
 obtaining a multi-crystalline substrate consisting essentially of doped metallurgical grade silicon of purity of 99.9%-99.999% doped to a first type of conductance;   forming a diffusion layer on top surface of the substrate such that the diffusion layer has opposite conductance of the first type; and,   forming a first thin-film structure over and in contact with the diffusion layer.   
     
     
         16 . The method of  claim 15 , further comprising forming a second thin-film structure over the first thin-film structure. 
     
     
         17 . The method of  claim 16 , wherein forming a first thin film structure comprises:
 forming a first intrinsic layer over and in contact with the diffusion layer; and,   forming a first doped layer of same conductance of the first type over and in contact with the intrinsic layer.   
     
     
         18 . The method of  claim 16 , wherein forming a second thin-film structure over the first thin-film structure comprises forming a thin-film p-i-n junction.