Study of structural and optical properties of kesterite Cu2ZnGeX4 (X = S, Se) thin films synthesized by chemical spray pyrolysis

Abstract

We report on the fabrication of polycrystalline Cu₂ZnGeX₄ (X = S, Se) thin films using spray pyrolysis followed by post-sulfurization and post-selenization. The stoichiometric, morphological, structural and optical properties of fabricated thin films were investigated and discussed in the photovoltaic aspect. Although the as-sprayed films were observed to be grown with poor crystalline texture, the crystallinity was found to be greatly improved after post-sulfurization and post-selenization, which was confirmed by X-ray diffraction (XRD) and Raman spectroscopy. The band gap energy was estimated as 1.88–1.93 eV for post-sulfurized Cu₂ZnGeS₄ (CZGS) films and 1.40–1.43 eV for post-selenized Cu₂ZnGeSe₄ (CZGSe) films by UV-Vis absorption measurements. The crystal lattice parameters calculated from XRD patterns for post-sulfurized CZGS and post-selenized CZGSe films were found to be consistent with kesterite structure which is strongly supported by the band gap energy estimated from the UV-Vis absorption measurements.