Cu-In-Ga metal precursors sputter deposited from a single ternary target for Cu(lnGa)(SeS)2 film formation

Precursor films used for the growth of Cu(InGa)Se₂ were sputter deposited from a single Cu-In-Ga compound target to determine if better control of composition and improved reproducibility compared to precursors deposited from separate sputter targets could be obtained. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize changes in phase and morphology of the ternary sputter target, precursor films, and reacted films over a series of deposition runs and compared with films deposited from two targets. The surface morphology and composition of the target and precursor films were characterized over a range of sputtering conditions and compared to the bulk target composition over time. The precursor films contain Cu₉(In_1-xGa_x)₄ and In phases with In-rich nodules. The target has a Cu-rich surface composition compared to the bulk that indicates preferential sputtering of In. Cu(InGa)(SeS)₂ films were formed by a three-step H₂Se/Ar/H₂S reaction process. The composition of reacted films using ternary target precursors is comparable to the bulk target composition and good reproducibility is demonstrated. Finally, solar cells fabricated using the reacted films gave a maximum efficiency of 13.4%.