Correlative spectroscopy mapping of the prospective photovoltaic material bournonite using Raman and cathodoluminescence

The polar material bournonite (CuPbSbS3) is of interest as a new absorber layer for thin-film photovoltaics. At present, efficiencies are low and there is a lack of fundamental knowledge on the structural and optoelectronic properties of the material in thin-film form. In this study, we report complete experimental Raman spectra, which are interpreted with the help of ab initio calculations. Raman maps reveal variation of relative peak intensities both within grains and across grains as most likely caused by crystal anisotropy. We also present correlated hyperspectral cathodoluminescence (CL) results and observe a red shift of the CL peak wavelength of 5 to 15 nm at the bournonite grain boundaries. Transmission electron microscopy reveals Cu enrichment along grain boundaries that, together with CuPb antisite and interstitial Cu point defect formation, is proposed to cause the luminescence red shift.