Raman scattering quantitative analysis of the anion chemical composition in kesterite Cu₂ZnSn(S_xSe_1−x)₄ solid solutions

Highlights: • An optical method for the quantitative measurement of [S]/([S] + [Se]) in CZTSSe is presented. • It is based on Raman spectroscopy and covers whole S–Se range of compositions. • The proposed method is independent of crystal quality, experimental conditions and type of material. • The validity of the technique is proven by comparison with independent composition measurements (XRD and EQE). • Test of the method on the data published in the literature has given satisfactory results. - Abstract: A simple and non destructive optical methodology for the quantitative measurement of [S]/([S] + [Se]) anion composition in kesterite Cu₂ZnSn(S_xSe_1−x)₄ (CZTSSe) solid solutions by means of Raman spectroscopy in the whole S–Se range of compositions has been developed. This methodology is based on the dependence of the integral intensity ratio of Raman bands sensitive to anion vibrations with the [S]/([S] + [Se]) composition of the kesterite solid solutions. The calibration of the parameters used in this analysis involved the synthesis of a set of CZTSSe powders by solid state reaction method, spanning the range from pure Cu₂ZnSnS₄ to pure Cu₂ZnSnSe₄. The validity of the methodology has been tested on different sets of independent samples, including also non-stoichiometric device grade CZTSSe layers with different compositions and films that were synthesized by solution based processes with different crystalline quality. In all cases, the comparison of the results obtained from the analysis of the intensity of the Raman bands with independent composition measurements performed by different techniques as X-ray diffraction and external quantum efficiency has confirmed the satisfactory performance of the developed methodology for the quantitative analysis of these compounds, independently on the crystal quality or the method of synthesis. Further strong support on the methodology performance has been obtained from the analysis of a wider range of samples, including nanocrystals, monograins, powders and thin films, which Raman spectra and anion compositions were reported in the literature. The agreement of the values of [S]/([S] + [Se]) obtained from the analysis of the Raman spectra published in the literature with the compositions reported for these samples demonstrate the validity of the developed methodology for the chemical analysis of these compounds, independently of the experimental conditions of the measurements and of the type of samples