In-Situ Investigation on Selenization Pathways of Bilayer Stacked Cu-Zn-Sn Metal Precursors Designed for Reduced Sn Loss

Bilayer Cu-Zn-Sn precursors, i.e., Mo/Zn/(Cu + Sn), and Mo/Sn/(Cu + Zn), were prepared using the simultaneous and sequential sputtering of pure Cu, Sn and Zn targets. Their phase evolutions during subsequent selenization were examined by in-situ high-temperature X-ray diffraction (XRD). Both XRD and Raman scattering techniques were used to confirm the formation of quaternary Cu2ZnSnSe4 (CZTSe). The results showed that the Mo/Sn/(Cu + Zn) precursors were transformed completely to CZTSe at approximately 375 degrees C and higher, whereas the complete transformation of the Mo/Zn/(Cu + Sn) precursor required higher temperatures (400-450 degrees C). Furthermore, the precursor structure with co-sputtered Cu and Sn elements was preferred to prevent severe Sn loss during CZTSe formation at and above 450 degrees C.