Optical and structural properties of Fe- and Ge-substituted CZTS thin films produced by alternating sputtering deposition

Utilizing the DC magnetron sputtering technique in conjunction with a Cu₂ZnSnS₄ (CZTS) and metal Fe (or Ge) target through an alternating sputtering deposition process (CZTS/Fe/CZTS/Fe/CZTS) followed by vulcanization, we successfully synthesized Fe- and Ge-substituted CZTS thin films. The phase structure and optical properties of these films were characterized using X-ray diffraction (XRD), Raman spectroscopy, and UV-Vis spectroscopy. Our results indicate that by precisely controlling the thickness of the Fe and Ge interlayers, high-quality Fe- and Ge-substituted CZTS thin films can be produced. The analysis reveals that Fe substitution enhances absorbance in the long-wavelength region of the visible spectrum. Conversely, Ge substitution does not significantly affect absorbance in the long-wavelength region but decreases optical absorbance at wavelengths shorter than 700 nm. Adjustments in the band gap are achievable with Ge and Fe substitutions within a 50 nm range. However, an excess of Fe and Ge may result in the formation of secondary phase structures, specifically FeS₂ and SnS₂, without altering the band gap.