Electron microscopy study of individual grain boundaries in Cu2ZnSnSe4 thin films

We study the structural, chemical, and electronic properties of individual grain boundaries in Cu₂ZnSnSe₄ (CZTSe) using combined electron microscopy techniques including scanning electron microscopy-based cathodoluminescence (CL)-spectrum imaging and scanning transmission electron microscopy-based Z-contrast imaging and energy-dispersive spectroscopy profiling. Two representative grain boundaries have been studied. We find that the grain boundary that exhibits a redshift in the CL spectrum image is found to link to a ZnSe second phase. The grain boundary showing no redshift in the CL spectrum image is not linked to any secondary phase. The stability of CZTSe cross-section samples with storage time is also discussed.