Structure and phase composition of sputter deposited (Ag,Cu)(In,Ga)Se2 thin film solar cells

Abstract

The addition of Ag to Cu(InGa)Se2 (CIGS) has shown benefits including improved process tolerance and potential for improved device performance. Here, we studied the structure and phase composition of sputter-deposited ACIGS thin films using X-ray diffraction (XRD), glancing incidence XRD (GIXRD) analyzed by Rietveld refinement, and Raman spectroscopy. Samples were deposited on stainless steel substrates with different back electrode selenization and absorber growth temperatures. XRD analysis showed that Ag-alloying of CIGS films led to splitting of the (220)/(204) and (312)/(116) peaks while they overlapped in a CIGS sample. Raman spectroscopy indicated formation of an ordered defect phase (ODC) for Ag-alloyed samples. The average A1/ODC peak area ratio was similar for the different growth temperatures but increased with reduced back electrode selenization. The sample with no K incorporation shows the highest A1/ODC area. Comparing the A1 Raman mode of the chalcopyrite phase at the surface and back-side of the absorber layer indicates that the higher absorber growth temperature lowered the Ga/III variation at the surface and the back of the film.