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

Abstract

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] ≈ 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.

A mechanochemical route to single phase Cu2ZnSnS4 powder

“…The spectra of the binary phases CuS, ZnS, and SnS as well as that of CZTS are depicted in Figure 6. As already shown in [7] the spectra significantly differ from each other. Therefore it is possible to identify secondary phases in CZTS samples.…”

“…Finally the integral chemical composition can be calculated as Furthermore, phase purity was investigated by XANES. As explained in [7], X-ray absorption near edge structure analysis at the sulfur K-edge (2472 eV) gives information about the chemical environment of the selected atom, in this case sulfur, the electronic density of the unoccupied states, and the local crystal structure. It can be considered as a fingerprint for the identification of different materials [33].…”

“…Therefore it is possible to identify secondary phases in CZTS samples. To perform a quantitative analysis of the secondary phases the measured spectrum was compared to a reference sample which can be assumed to be single phase CZTS and was already measured in [7]. The spectrum was fitted with a linear combination of the reference spectrum and the spectra of CuS, SnS, and ZnS.…”

“…Systematic analysis of the semiconductor compound and its structural, chemical, and physical properties has been in the focus of interest in the last few years [5][6][7][8][9][10]. Due to the formation of secondary phases it is challenging to prepare phase-pure CZTS powder, which is important for detailed experiments concerning the correlations between structural and electronic properties.…”

“…Due to its small enthalpy of formation ZnS is likely to form and has been found to have a detrimental influence on solar cell performance. [7,8,20] Identification and quantification of the secondary phases ZnS and Cu 2 SnS 3 by X-ray and neutron diffraction is difficult because of diffraction pattern overlap. As reported in [7] it is possible to identify the most important secondary phases with X-ray absorption spectroscopy (XAS).…”