Determination of secondary phases in kesterite Cu2ZnSnS4 thin films by x-ray absorption near edge structure analysis

Secondary phases in Cu2ZnSnS4 (CZTS) are investigated by x-ray absorption spectroscopy. Evaluating the x-ray absorption near edge structure at the sulfur K-edge, we show that secondary phases exhibit sufficiently distinct features to allow their quantitative determination with high accuracy. We are able to quantify the ZnS fraction with an absolute accuracy of +/- 3%, by applying linear combination analysis using reference spectra. We find that even in CZTS thin films with [Sn]/[Zn] approximate to 1, a significant amount of ZnS can be present. A strong correlation of the ZnS-content with the degradation of the electrical performance of solar cells is observed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3671994]