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.