Patent ID: 8889468

Claim:
A method for fabricating a tandem photovoltaic cell, comprising: forming a bifacial top cell, comprising: providing a top first transparent conductive oxide material; forming a top window material underlying the top first transparent conductive oxide material; forming a first interface region between the top window material and the top first transparent conductive oxide material, the first interface region being substantially free from one or more entities from the top first transparent conductive oxide material being diffused into the top window material; forming a top absorber material underlying the top window material, the top absorber material comprising a copper species, an indium species; subjecting the top absorber material to a thermal treatment process in a sulfur-containing environment, wherein the thermal treatment process includes a temperature ramp rate ranging from about 10 degrees Celsius/second to about 50 degrees Celsius/second; forming a top second transparent conductive oxide material underlying the top absorber material; forming a second interface region between the top second transparent conductive oxide material and the top absorber material, the second interface region being substantially free from one or more entities from the top first transparent conductive oxide material being diffused into the top absorber material, wherein the second interface region comprises at least one material selected from the group consisting of platinum, titanium, chromium, and silver; forming a bottom cell, comprising: forming a bottom first transparent conductive oxide material; forming a bottom window material underlying the first bottom transparent conductive oxide material; forming a bottom absorber material underlying the bottom window material; forming a bottom electrode material underlying the bottom absorber material; and forming a coupling layer between the bifacial top cell and the bottom cell, the coupling layer being free from a parasitic junction between the bifacial top cell and the bottom cell.