In Situ Raman Monitoring of Cu2ZnSnS4 Oxidation and Related Decomposition at Elevated Temperatures

In this work, we report the results of in situ Raman monitoring of copper zinc tin sulfide [Cu ₂ZnSnS₄ (CZTS)], phase under relevant processing conditions at elevated temperatures. CZTS films are prepared from a simple sol-gel method, followed by sulfurization. Raman microspectroscopy measurements are carried out using a 514.5-nm excitation laser on CZTS samples at room temperature and under in situ conditions in sealed chamber and in open air at elevated temperatures. Preliminary results of in situ Raman showed that CZTS phase is Raman active at elevated temperatures up to ~600 °C. In addition, important information regarding CZTS phase oxidation and related decomposition at high temperatures is revealed. Coupled with X-ray diffraction analysis of the in situ Raman examined CZTS samples, a two-step oxidation/decomposition reaction is suggested. CZTS oxidizes first at ~400 °C to form tin oxide (SnO) and binary sulfides mainly copper sulfide (Cu_2-xS) and zinc sulfide (ZnS). Then, at temperatures higher than 400 °C, the remaining sulfides oxidize to form zinc oxide (ZnO) and copper sulfate (CuSO₄). The study demonstrates that in situ Raman, combined with other ex situ characterization techniques, could provide valuable insights that help understand the complex processes involving phase formation and degradation for CZTS and other related chalcogenides as solar absorber materials.