Effect of post-sulfurization on the composition, structure and optical properties of Cu ₂ ZnSnS ₄ thin films deposited by sputtering from a single quaternary target

Quaternary Cu ₂ ZnSnS ₄ (CZTS) thin films were deposited on heated glass substrates directly from a non-stoichiometric quaternary CZTS target by radio-frequency (RF) magnetron sputtering process, followed by post-sulfurization in atmosphere of Ar + H ₂ S(5%). The results of X-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM) show that post-annealed process can improve the crystallinity of CZTS thin films. Both XRD and Raman spectra analysis indicate the internal compressive stress relaxes in post-annealed CZTS thin films. Further transmission spectra demonstrate that the band gaps of post-annealed CZTS thin films are smaller than those of as-deposited due to the relaxation of internal compressive stress and the increase of Cu content in the post-annealed CZTS films.