Ag-Cu-In-Ga Metal Precursor Thin Films for (Ag, Cu)(In, Ga)Se2 Solar Cells

The Ag-Cu-In-Ga (ACIG) material system has been investigated over a composition range used for reaction to form (Ag, Cu)(In, Ga)Se-2 thin films for photovoltaic application. ACIG thin films were sputter deposited from Ag0.77Ga0.23, Cu0.77Ga0.23, and In targets using different layer sequences with Ag/(Cu + Ag) and (Ag + Cu)/(Ga + In) ratios fixed at 0.25 and 0.90, respectively. The most uniform morphology was achieved with a Ag-Ga layer followed by a layer with co-sputtered Cu-Ga and In. Varying the sputtering sequence for stacked layers resulted in dissimilar morphologies and structural phases. X-ray diffraction analyses revealed that Ag-Ga and In layers intermix to form the (Ag, Cu) In-2 phase in all Ag-containing samples except one with a (Ag) over bar -Ga/Cu-Ga/In sequence. In addition, precursors were shown to be unstable during storage at room temperature, where a secondary (Ag, Cu*) In-2 phase with higher Cu content formed. Finally, phase composition of the precursors annealed at 300 degrees C was characterized.