Control of oxygen for magnetron sputtered ZnO:Al window layer in Cu(In,Ga)Se2 thin film solar cells

In this study, aluminum doped zinc oxide (ZnO:Al) thin films were prepared by magnetron sputtering from a ceramic target at room temperature for application in Cu(In,Ga)Se-2 (CIGS) thin film solar cells as a window layer. Different oxygen-argon mixture gas fluxes (5% O-2 in Ar) were input in the deposition chamber during the preparation of ZnO:Al thin films. The influences of oxygen content on different properties of sputtered ZnO:Al thin films, including grain structure, optical and electrical properties, were systematically investigated. High O-2-Ar mixture gas flux leads to a low dynamic deposition rate, a high light transmission and a high resistivity. The CIGS thin film solar cells show a high short circuit current density but a low fill factor when ZnO:Al window layer is prepared at a high O-2-Ar mixture gas flux, which is related to the enhanced transmission and resistivity of ZnO:Al thin films with an increasing O-2-Ar mixture gas flux. The highest efficiency CIGS thin film solar cell of 14.7% has been achieved with the structure of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al/(Ni/Al/Ni)grids/MgF2 when the O-2-Ar mixture gas flux is 1.5sccm here.