Fabrication of Cu2ZnSnS4 thin films using a ceramic quaternary target

Cu2ZnSnS4 (CZTS) films were fabricated from a ceramic quaternary target, through middle frequency magnetron sputtering. A post sulfurization process was applied for the sputtered films and sulfurization temperatures ranging from 460 °C to 580 °C were utilized. It has been found that obvious Zn loss exists during the sputtering, making the sputtered films become Zn poor although the target is Zn rich. The sputtered films were not totally amorphous, but composed of small CZTS grains at the size of several nanometers. After a post sulfurization process the crystallinity were greatly improved and films composed of densely packed CZTS grains at the size of several hundred nanometers can be obtained at sulfurization temperatures higher than 520 °C. Yet minor SnS coexists with CZTS since the films were Zn poor and Sn rich. And finally the CZTS films sulfurized at 580 °C depict an optical band gap of around 1.55 eV.