Method and structure for thin film tandem photovoltaic cell

Abstract

A tandem photovoltaic cell. The tandem photovoltaic cell includes a bifacial top cell and a bottom cell. The top bifacial cell includes a top first transparent conductive oxide material. A top window material underlies the top first transparent conductive oxide material. A first interface region is disposed between the top window material and the top first transparent conductive oxide material. The first interface region is substantially free from one or more entities from the top first transparent conductive oxide material diffused into the top window material. A top absorber material comprising a copper species, an indium species, and a sulfur species underlies the top window material. A top second transparent conductive oxide material underlies the top absorber material. A second interface region is disposed between the top second transparent conductive oxide material and the top absorber material. The bottom cell includes a bottom first transparent conductive oxide material. A bottom window material underlies the first bottom transparent conductive oxide material. A bottom absorber material underlies the bottom window material. A bottom electrode material underlies the bottom absorber material. The tandem photovoltaic cell further includes a coupling material free from a parasitic junction between the top cell and the bottom cell.

What is claimed is: 
     
         1 . A method for fabricating a tandem photovoltaic cell, comprising:
 forming a first cell comprising:
 forming a first transparent conductive oxide layer; 
 forming a first absorber layer over the first transparent conductive oxide, the first absorber layer comprising a copper species, an indium species, and a sulfur species; 
 forming a first window layer over the first absorber layer; and 
 forming a second transparent conductive oxide layer over the first window layer; 
   forming a second cell comprising:
 forming a first electrode layer; 
 forming a second absorber material over the first electrode layer; 
 forming a second window layer over the second absorber layer; and 
 forming a third transparent conductive oxide layer over the second window layer; 
   forming a coupling layer overlying the second transparent conductive oxide layer; and   coupling the first cell with the second cell.   
     
     
         2 . The method of  claim 1  wherein the first transparent conductive oxide comprises indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:Al), or Fluorine doped tin oxide (SnO 2 :F). 
     
     
         3 . The method of  claim 1  wherein the first window material comprises cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenium (ZnSe), zinc oxide (ZnO), or zinc magnesium oxide (ZnMgO). 
     
     
         4 . The method of  claim 1  wherein the first absorber material comprises copper indium disulfide (CIS), copper indium aluminum disulfide, copper indium gallium disulfide (CIGS), or (Ag,Cu)(In,Ga)S2. 
     
     
         5 . The method of  claim 1  wherein the second transparent conductive oxide material comprises cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenium (ZnSe), zinc oxide (ZnO), or zinc magnesium oxide (ZnMgO). 
     
     
         6 . The method of  claim 1  wherein the third transparent conductive oxide material comprises cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenium (ZnSe), zinc oxide (ZnO), or zinc magnesium oxide (ZnMgO). 
     
     
         7 . The method of  claim 1  wherein the second window material comprises cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenium (ZnSe), zinc oxide (ZnO), or zinc magnesium oxide (ZnMgO). 
     
     
         8 . The method of  claim 1  wherein the second electrode material comprises a transparent conductive oxide material or a metal material. 
     
     
         9 . The method of  claim 1  wherein the second absorber material comprises a copper indium disulfide thin film material, a copper indium aluminum disulfide thin film material, or a copper indium gallium disulfide material. 
     
     
         10 . The method of  claim 1  wherein the second absorber material comprises Cu 2 SnS 3 ; Cu(In,Ga)Se 2 ; CuInSe 2 ; or FeSi 2 . 
     
     
         11 . The method of  claim 1  further comprising subjecting the first absorber material to a thermal treatment process, wherein the thermal treatment process includes increasing the temperature with a temperature ramp rate ranging from about 10 degrees Celsius/second to about 50 degrees Celsius/second. 
     
     
         12 . The method of  claim 11  wherein the thermal treatment process is conducted in a sulfur-containing environment. 
     
     
         13 . The method of  claim 1 , wherein forming the first cell further includes:
 forming a first interface region between the first transparent conductive oxide layer and the first absorber layer; and   forming a second interface region between the second transparent conductive oxide material and the first window layer, the second interface region being substantially free from one or more entities from the second transparent conductive oxide layer and the first window layer.   
     
     
         14 . The method of  claim 13  wherein the second interface region comprises at least one material selected from the group consisting of platinum, chromium, and silver. 
     
     
         15 . The method of  claim 1  wherein the coupling layer comprises an optically transparent material. 
     
     
         16 . The method of  claim 1  wherein the coupling layer comprises ethyl vinyl acetate. 
     
     
         17 . A method for fabricating a tandem photovoltaic cell comprising:
 providing a substrate having a top surface and a bottom surface;   forming a first electrode layer over the top surface of the substrate;   forming a first absorber layer over the first electrode layer;   forming a first window layer over the first absorber layer;   forming a second electrode layer over the first window layer;   forming a coupling layer over the second electrode layer;   forming a third electrode layer over the coupling layer;   forming a second absorber layer over the third electrode layer;   forming a second window layer over the second absorber layer; and   forming a fourth electrode layer over the second window layer.   
     
     
         18 . The method of  claim 17 , further comprising:
 forming a first interface region between the third electrode layer and the second absorber material, the first interface region being substantially free from one or more entities from the third electrode layer being and the second absorber layer; and   forming a second interface region between the fourth electrode layer and the second window material, the second interface region being substantially free from one or more entities from the fourth electrode layer and the second window material.   
     
     
         19 . The method of  claim 17 , wherein the coupling layer comprises ethyl vinyl acetate.