Fabrication of Cu₂ZnSnS₄ absorbers by sulfurization of Sn-rich precursors

Cu₂ZnSnS₄ (CZTS) absorbers were grown by sulfurization of the Sn-rich precursors that were cosputtered from a CuSn target (2 in.) and a ZnS target (2 in.). The excess Sn in the precursor could limit the decomposition of CZTS during the long sulfurization process at 510 °C. The sulfurized CZTS film cosputtered with CuSn 45 W and ZnS 70 W exhibits the intended bandgap of 1.53 eV, main Raman mode at 335.5 cm^-1 and a slightly Sn-rich composition. As the sputtering power of the CuSn target was increased from 45 to 60 W, the corresponding films consisted of a CZTS phase and several Sn-rich phases (SnS/Sn₂S₃/Cu₄Sn ₇S₁₆). Conversely, when this sputtering power was reduced to 35 W, the resultant film consisted of a CZTS phase and a ZnS secondary phase. Besides, Raman scattering shows that the increased sputtering power of the CuSn target is related with the redshift and the increased FWHMs of primary Raman modes for the resultant films. X-ray diffraction data show the (112)-oriented growth and lattice expansion for the obtained CZTS films.