Advanced characterization of electrodeposition-based high efficiency solar cells: Non-destructive Raman scattering quantitative assessment of the anion chemical composition in Cu(In,Ga)(S,Se)2 absorbers

This work reports a detailed comparative study of electrodeposition-based (ED) cells fabricated with S-free Cu(In,Ga)Se2 and S-containing Cu(In,Ga)(S,Se)2 absorbers. ED based processes have a strong interest, because of their potential for cost reduction. ED of metal precursors followed by Rapid Thermal Process (RTP) with elemental Se and S has demonstrated to successfully obtain 60×120 cm2 modules up to 14% aperture area (AA) efficiency. In this work, the impact of the presence of S in the surface region of the absorbers is analyzed in detail. The results show the possibility to obtain high efficiency, reproducible cells by careful control of this parameter, which is assessed by Raman scattering. Standard techniques for surface S content measurement are limited due to either overall composition estimation (X-ray diffraction), overlap of S and Mo signals (X-ray fluorescence) or their need for handling samples under vacuum conditions and/or their destructive character (inductively coupled plasma mass spectroscopy, secondary ions mass spectroscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy…). In this framework Raman scattering is interesting as it is non-destructive and very sensitive to both composition and crystal quality. This work proposes a Raman scattering based methodology for the quantitative analysis of the anion composition ratio in the surface region of the absorbers, providing with a simple non-destructive assessment procedure of this relevant parameter.