Sodium doped thin film cigs/cigss absorber for high efficiency photovoltaic devices and related methods

Abstract

A method of processing a thin-film absorber material with enhanced photovoltaic efficiency. The method includes providing a soda-lime glass substrate having a surface region and forming a barrier material overlying the surface region, followed by formation of a stack structure including a first thickness of a first precursor, a second thickness of a second precursor, and a third thickness of a third precursor. The first thickness of the first precursor is sputtered with a first target device including a first mixture of copper, gallium, and a first sodium species. The method further includes subjecting the soda-lime glass substrate having the stack structure in a thermal treatment process with at least H 2 Se gas species at a temperature above 400° C. to cause formation of an absorber material. Moreover, the method includes transferring a second sodium species from a portion of the soda-lime glass substrate via gas-phase diffusion during the thermal treatment process.

What is claimed is: 
     
         1 . A method of processing a thin film absorber material with enhanced photovoltaic efficiency, the method comprising:
 forming a barrier material overlying a surface of a substrate comprising sodium, the barrier material configured to prevent a diffusion of sodium ions from the substrate;   forming a back electrode comprising molybdenum over the barrier material;   depositing at least one layer of material over the back electrode;   subjecting the substrate having the at least one layer of material to a thermal treatment process in the presence of H 2 Se gas and nitrogen at a temperature above 400° C. to form an absorber material; and   transferring, during the subjecting operation, a sodium species from a sodium source into the absorber material.   
     
     
         2 . The method of  claim 1  wherein the barrier material is selected from silicon dioxide, silicon nitride, or silicon oxynitride. 
     
     
         3 . The method of  claim 1  wherein the step of transferring a sodium species comprises,
 reacting a sodium species from a second substrate comprising sodium using the H 2 Se gas species to from an intermediary species of Na 2 Se; 
 contacting the Na 2 Se to the absorber material; and 
 absorbing sodium from the Na 2 Se into the absorber material. 
 
     
     
         4 . The method of  claim 3  wherein the sodium has a concentration of 10 18 -10 19  atoms/cc in the absorber material. 
     
     
         5 . The method of  claim 3  wherein the intermediary species of Na 2 Se is a gas phase species. 
     
     
         6 . The method of  claim 3  wherein the absorber material includes from 0.7 at % to 1.5 at % of sodium. 
     
     
         7 . The method of  claim 3  wherein the absorber material includes an atomic ratio of copper species to indium species and gallium species at about 0.9. 
     
     
         8 . The method of  claim 1  wherein the step of subjecting the soda lime glass substrate and the at least one layer of material comprises heating to a temperature from about 400° C. to about 600° C. 
     
     
         9 . A method of incorporating sodium species into a thin-film photovoltaic absorber, the method comprising:
 providing a plurality of substrates comprising sodium, each having a first surface region;   forming a bottom electrode material overlying the first surface region of each substrate;   forming a stack material layers including copper, indium, gallium, and sodium, overlying the bottom electrode material at a first temperature;   disposing the plurality of substrates in a furnace containing H 2 Se gas and nitrogen gas; and   heating the plurality of soda lime glass substrates to a second temperature to cause the precursor materials on each substrate to react with selenium from the H 2 Se gas to form a photovoltaic absorber material having sodium from the precursor materials and from one or more of the plurality of substrates.   
     
     
         10 . The method of  claim 9  wherein each of the plurality of substrates is a standard commercial soda lime flat glass with about 14 wt % of Na 2 O. 
     
     
         11 . The method of  claim 9  wherein sodium from one or more of the plurality of substrates is provided in an intermediary species of Na 2 Se in gas phase. 
     
     
         12 . The method of  claim 9  wherein the first temperature comprises a temperature from about 20° C. to about 100° C. 
     
     
         13 . The method of  claim 9  wherein the second temperature comprises a temperature from about 400° C. to about 600° C. 
     
     
         14 . The method of  claim 9  wherein the photovoltaic absorber material comprises a copper-indium-gallium-selenium compound having sodium of about 0.7 at % to 1.5 at %.