Effect of selenization pressure on CuInSe2 thin films selenized using co-sputtered Cu-In precursors

CuInSe2 thin films were formed from the selenization of co-sputtered Cu–In alloy layers. These layers consisted of only two phases, CuIn2 and Cu11In9, over broad Cu–In composition ratio. The concentration of Cu11In9 phase increased by varying the composition from In-rich to Cu-rich. The composition of co-sputtered Cu–In alloy layers was linearly dependent on the sputtering power of Cu and In targets. The metallic layers were selenized either at a low pressure of 10 mTorr or at 1 atm Ar. A small number of Cu–Se and In–Se compounds were observed during the early stage of selenization and single-phase CuInSe2 was more easily formed in vacuum than at 1 atm Ar. Therefore, CuInSe2 films selenized in vacuum showed smoother surface and denser microstructure than those selenized at 1 atm. The results showed that CuInSe2 films selenized in vacuum had good properties suitable for a solar cell.