CIGS solar cells using a novel window Zn/sub 1-x/Mg/sub x/O film

The authors propose a new window layer of Zn/sub 1-x/Mg/sub x/O thin films with a controllable bandgap as an alternative window layer to a CdS film. Measurements of valence band offset and bandgap indicate that a conduction band offset of Zn/sub 1-x/Mg/sub x/O/CIGS layers can be controlled by Mg content of the Zn/sub 1-x/Mg/sub x/O film. They fabricated CIGS solar cells consist of an ITO/Zn/sub 1-x/Mg/sub x/O/CIGS/Mo/Glass structure. The Zn/sub 1-x/Mg/sub x/O/CIGS solar cells show performance close to that of the cells using CdS films, when the conduction band of Zn/sub 1-x/Mg/sub x/O is higher than that of CIGS. An appropriate conduction band offset of Zn/sub 1-x/Mg/sub x/O/CIGS layers decreases the recombination via defects at the interface between majority carriers. Control of conduction band offset has an effect on improving an efficiency of Cd free CIGS solar cells.