Effect of sputtering conditions of co-sputtered Cu–In–Ga precursors on Cu(InGa)Se2 photovoltaic absorber formation

•Increasing the sputtering power of CuGa and In targets reduced film density.•The selenization rate of CuGaIn increased significantly by reducing precursor density.•Selenization mechanism of CuGaIn was confirmed by in-situ high-temperature XRD.

CuGa and In targets were simultaneously deposited onto Mo-coated low-alkali glass with different sputtering powers, such as 15 W–CuGa/40 W–In (Case I) and 70 W–CuGa/85 W–In (Case II), to control the stacking density and thickness of CuGaIn precursor films. Precursors were then selenized in a tube-type rapid thermal processing system under a Se atmosphere. Temperature-dependent phase evolution during the selenization of each precursor has been investigated by in situ high-temperature X-ray diffraction technique. Comparison of the isothermal scan results at 300 °C indicated that the Case II precursor fabricated using a higher sputtering power was selenized faster than the Case I precursor prepared using a lower sputtering power. Another set of experiments using precursors with different Cu/III atomic ratio was also performed. It was concluded that the compositional change in the CuGaIn precursor in the range of Cu/III = 0.78–1.06 and Ga/III = 0.24–0.32 at the given sputtering conditions (e.g., CuGa power = 70 W and In power = 70–100 W) did not affect the selenization rate significantly.