The preparation of Cu(In,Al)S2 films by direct reduction and sulfuration of the oxide precursors

We report the preparation of Cu(In,Al)S2 (CIAS) films by direct reduction and sulfuration of the oxide precursors, and propose that this is a promising approach for application in solar cells. The CIAS films with a single chalcopyrite phase clearly show a “sandwich” structure. Typical near-stoichiometric slightly S-poor films with two energy band gaps (Eg1 = 1.0 eV, Eg2 = 1.4 eV) are also obtained, which shows that the sulfuration process is incomplete and that the Eg can be increased by alloying aluminum and sulfur.