Effect of precursors pre-annealing on the microstructure of Cu2ZnSnS4 thin films on titanium foil substrate

Abstract

Cu2ZnSnS4 (CZTS) thin films were synthesized by sulfurization of Cu/Sn/Cu/Zn precursors electrochemically deposited on titanium foil substrates. A part of the precursor samples were pre-annealed at 250 °C for 30 min. Sulfurization of the samples was carried out at 500 °C for 2 h. It was obtained that preliminary annealing leads to exclusions of CuSn and CuZn4 phases from the precursor composition. When using the as-deposited precursors, the CZTS phase is formed with preferred orientation along the [211] and [213] directions, and petal-shaped crystallites on the film surface form. Using annealed precursor films, the CZTS phase is formed with porous morphology and without pronounced preferred orientation. The CZTS films obtained from as-deposited precursors contain lack of tin (Cu/(Sn + Zn) = 0.95 and Zn/Sn = 1.95 ratios of at.%), whereas the annealed precursor lead to formation of the films with elemental composition close to stoichiometry (Cu/(Sn + Zn) = 1.13 and Zn/Sn = 1.06 ratios of at. %). The films obtained from annealed precursors possess lattice parameters close to the data for bulk crystals, which indicates high structural perfection of CZTS.