Method of Fabricating High Efficiency CIGS Solar Cells

Abstract

A method for fabricating high efficiency CIGS solar cells including the deposition of Ga concentrations (Ga/(Ga+In)=0.25−0.66) from sputtering targets containing Ga concentrations between about 25 atomic % and about 66 atomic %. Further, the method includes a high temperature selenization process integrated with a high temperature anneal process that results in high efficiency.

What is claimed: 
     
         1 . A solar cell, comprising:
 a back contact layer disposed on a substrate;   an absorber layer formed above the back contact layer;   wherein the absorber layer comprises a first layer comprising In, a second layer comprising Cu formed above the first layer, and a third layer comprising between approximately 25 and 60 atomic % Ga formed above the second layer;   a buffer layer formed above the absorber layer;   a front contact interface layer formed above the buffer layer; and   a front contact layer formed above the front contact interface layer.   
     
     
         2 . The solar cell of  claim 1 , wherein the absorber layer comprises approximately 60 atomic % Cu and about 40 atomic % Ga. 
     
     
         3 . The solar cell of  claim 1 , wherein the thickness of the back contact layer is in a range between 0.3 micrometers and 1 micrometer. 
     
     
         4 . The solar cell of  claim 1 , wherein the buffer layer is n-type. 
     
     
         5 . The solar cell of  claim 1 , wherein the substrate comprises at least one float glass, borosilicate glass, flexible glass, specialty glass for high temperature processing, stainless steel, carbon steel, aluminum, copper, titanium, molybdenum, polyimide, plastics, and cladded metal foils. 
     
     
         6 . The solar cell of  claim 1 , wherein the front contact interface layer includes intrinsic ZnO. 
     
     
         7 . The solar cell of  claim 1 , wherein the back contact layer comprises molybdenum. 
     
     
         8 . The solar cell of  claim 1 , wherein the thickness of the back contact layer is in a range between 0.3 micrometers and 1 micrometer. 
     
     
         9 . The solar cell of  claim 1 , wherein the absorber layer comprises sodium. 
     
     
         10 . The solar cell of  claim 1 , wherein the buffer layer comprises at least one of CdS, ZnS, In 2 S 3 , In 2 (S,Se) 3 , CdZnS, ZnO, Zn(O,S), and (Zn,Mg). 
     
     
         11 . The solar cell of  claim 1 , wherein the front contact layer comprises at least one of Al:ZnO, InSnO, InZnO, B:ZnO, Ga:ZnO, F:ZnO, and F:SnO 2 . 
     
     
         12 . A solar cell, comprising:
 a front contact layer disposed on a substrate;   a front contact interface layer formed above the front contact layer;   a buffer layer formed above the front contact interface layer;   an absorber layer formed above the buffer layer;   wherein the absorber layer comprises a first layer comprising Cu, a second layer comprising In formed above the first layer, and a third comprising between approximately 25 and 60 atomic % Ga formed above the second layer; and   a back contact layer formed above the absorber layer.   
     
     
         13 . The solar cell of  claim 12 , wherein the absorber layer comprises approximately 33.3 atomic % Cu and about 66.6 atomic % Ga. 
     
     
         14 . The solar cell of  claim 12 , wherein the thickness of the back contact layer is in a range between 0.3 micrometers and 1 micrometer. 
     
     
         15 . The solar cell of  claim 12 , wherein the buffer layer is n-type. 
     
     
         16 . The solar cell of  claim 12 , wherein the substrate comprises at least one float glass, borosilicate glass, flexible glass, specialty glass for high temperature processing, stainless steel, carbon steel, aluminum, copper, titanium, molybdenum, polyimide, plastics, and cladded metal foils. 
     
     
         17 . The solar cell of  claim 12 , wherein the absorber layer has a plurality of grain structures which exceed 1 micrometer in size. 
     
     
         18 . The solar cell of  claim 12 , wherein the absorber layer has a graded energy band structure. 
     
     
         19 . The solar cell of  claim 12 , wherein the absorber layer has a preferred crystal orientation in the (112) direction. 
     
     
         20 . The solar cell of  claim 12 , wherein the absorber layer comprises sodium.