Characterization of Cu2ZnSnS4 thin films on flexible metal foil substrates

The vacuum-based magnetron sputtering was utilized to the fabrication of Cu2ZnSnS4 (CZTS) thin films on flexible Al, Mo, and stainless steel foil substrates. The structural, compositional, and morphological properties of prepared thin films were investigated. According to the XRD and Raman results, for Al and Mo foil substrates, the structures of thin films are major CZTS and tiny secondary phase of Cu2SnS3. The preferred orientation of CZTS is along the (112) plane. The XRD peaks and Raman peaks of CZTS on Mo foil substrate are stronger than those on Al foil substrate. The calculated grain sizes are 33.6 and 39.0 nm for the thin films on Al and Mo foil substrates, respectively, indicating the higher crystallinity for Mo foil substrate samples. The compositions of thin films are near the stoichiometry of CZTS and show Cu-poor and Zn-rich properties. The surfaces of thin films are composed of compact grains. When using stainless steel foil as substrate, the fabricated thin films are composed of Cu2SnS3, FeS, and Zn, revealing the existence of sulfurization of Fe. The reaction between Fe and S inhibits the full sulfurization of Cu-Zn-Sn precursor, resulting in the absence of CZTS in the fabricated thin films. The composition of thin films is far from the stoichiometry of CZTS. In order to get desired properties of CZTS thin films, the inhibition of reaction between Fe and S is needed for stainless steel foil substrate.