Abstract
Direct current (DC) magnetron sputtering was employed to prepare Cu2ZnSnS4 (CZTS) thin films on soda-lime glass substrates from a ceramic quaternary CZTS target. The influences of DC power, substrate temperature and sulfurization temperature on the composition, crystal structure, surface morphology as well as the optical properties of the films were investigated. Crystalline Cu-poor and Sn-rich kesterite CZTS films were obtained directly from sputtering at a median power, above and below which films were both amorphous. While the film composition remained relatively unchanged with the substrate temperature up to 200 °C, increase of Sn content and decrease of Cu content were observed when the temperature further increased. Sputtering yield, atomic loss due to sublimation as well as the effects of operation conditions were used to explain such compositional change. A secondary phase, less uniform morphology as well as an increased band gap were observed simultaneously for these sputtered films with high Sn content. Sulfurization was carried out to further improve the crystallinity and optical properties of the sputtered CZTS films. An optimal sulfurization temperature of 550 °C was observed, where the film presented a pure CZTS phase, a maximum absorption coefficient (>104 cm−1) and a theoretic bandgap (1.55 eV).
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