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Grain-to-Grain Compositional Variations and Phase Segregation in Copper–Zinc–Tin–Sulfide Films

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journal contribution
posted on 18.08.2016, 00:00 authored by Alejandro Alvarez Barragan, Hoda Malekpour, Stephen Exarhos, Alexander A. Balandin, Lorenzo Mangolini
We have performed a rigorous investigation of the structure and composition of individual grains in copper–zinc–tin–sulfide (CZTS) films realized by sulfurization of a sputtered metal stack. Although on average close to the ideal CZTS stoichiometry, elemental analysis shows significant grain-to-grain variations in composition. High-resolution Raman spectroscopy indicates that this is accompanied by grain-to-grain structural variations as well. The intensity from the 337 cm–1 Raman peak, generally assigned to the kesterite phase of CZTS, remains constant over a large area of the sample. On the other hand, signals from secondary phases at 376 cm–1 (copper–tin–sulfide) and 351 cm–1 (zinc–sulfide) show significant variation over the same area. These results confirm the great complexity inherent to this material system. Moreover, structural and compositional variations are recognized in the literature as a factor limiting the efficiency of CZTS photovoltaic devices. This study demonstrates how a seemingly homogeneous CZTS thin film can actually have considerable structural and compositional variations at the microscale, and highlights the need for routine microscale characterization in this material system.