Comparative study of the influence of two distinct sulfurization ramping rates on the properties of Cu ₂ ZnSnS ₄ thin films

The Cu ₂ ZnSnS ₄ (CZTS) are produced by sulfurization of precursors cosputtering from Cu ₂ Sn and ZnS targets at two distinct ramping rates (2 °C/min and 21°C/min). Through the comparative analyses of scanning electron microscopy (SEM), energy dispersive of X-ray (EDS), X-ray diffraction (XRD), transmittance and Raman spectrum, it has been revealed that heating rate has a great impact on the reaction mechanism and characters of CZTS. The rapid heating rate 21°C/min has resulted in the appearance of bubble-like morphology and the concurrency of amorphous phases with CZTS. CZTS absorbers sulfurized at 2°C/min have exhibited a better crystallographic quality revealed by Raman spectroscopy and XRD pattern. However, XRD and transmittance have proved n-type SnS and Cu ₄ Sn ₇ S ₁₆ phases concurrent with the slowly ramped CZTS films. Difference in the two ramping rates has also resulted in the variance of band gap and Raman primary mode of the final films. The slow sulfurization (2°C/min) superior to the rapid one (21°C/min) is beneficial to the growth of the expected CZTS in this work.