Quantitative elemental analysis of photovoltaic Cu(In,Ga)Se2 thin films using MCs+ clusters


Kai Kaufmann, Fraunhofer Center for Silicon Photovoltaics CSP, Walter-Hülse-Straße 1, 06120 Halle, Germany.

E-mail: kai.kaufmann@csp.fraunhofer.de


In the process of optimizing solar cells, a quantitative and depth-resolved elemental analysis of photovoltaic thin films is strongly required. Regarding Cu(In,Ga)Se2 (CIGS) thin film solar cells, depth-dependent stoichometric changes of Ga and In are of great interest because the In/Ga ratio has a large effect on solar cell efficiencies. In this paper, we investigate the elemental composition of CIGS thin film solar cells based on secondary ion intensities in time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling, providing high sensitivities and high spatial resolution. Quantification of the data is obtained by comparison to X-ray photoelectron spectroscopy depth profiles. The detection of MCs+ clusters is used for semiquantitative elemental analysis of CIGS thin films. Correlation plots of the intensities of GaCs+ and InCs+ indicate that there is no relevant matrix effect for In and Ga due to changes in stoichiometry in the layer. Additional high-resolution inductively coupled plasma mass spectrometry measurements show a strong correlation between the ratio of the bulk concentrations of Ga and In and the ratio of integrated ToF-SIMS intensities of GaCs+ and InCs+ therefore supporting the quantitative interpretation of MCs+ data. Copyright © 2012 John Wiley & Sons, Ltd.