The goal of the Free-InCa project is the development and optimization of CuZnSn(S,Se)2 kesterite-based thin-film solar cells. Kesterite-based solar cells are composed of earth-abundant materials, which make them a promising candidate for low-cost thin-film solar cells.

However, the efficiency of kesterite-based solar cells is significantly lower than of other thin-film solar technologies. One culprit for the low efficiency is the high open-circuit voltage deficit, which limits the overall efficiency of this type of thin-film solar cells. Within the Free-InCa project, different preparation techniques and cell setups are evaluated together with high-level characterization techniques, to achieve an insight-driven improvement of the solar cell performance. 



A particular focus of these investigations are the interfaces within the solar cell. At the IPS and ITCP, the electronic and chemical structure at these interfaces (e.g., the absorber/buffer interface) are investigated. For this purpose, laboratory-based spectroscopy techniques, namely x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, and inverse photoemission spectroscopy (IPES), as well as x-ray-excited Auger electron spectroscopy are utilized.

In addition, synchrotron-based soft x-ray spectroscopies (x-ray absorption (XAS), x-ray emission spectroscopy (XES), and resonant inelastic x-ray scattering (RIXS)) are used at the synchrotron light source at KIT and the Advanced Light Source, Lawrence Berkeley National Laboratory, USA. In Fig. 2, the measurement setup at the ALS is exemplarily shown.



 Free-Inca is a BMBF (German Federal Ministry for Education and Research) funded project. The project partners are:

  • University of Oldenburg
  • Zentrum für Sonnenenergie- und Wasserstoffforschung Baden-Württemberg (ZSW)

Contact information: Dr. Dirk Hauschild, dirk hauschildWth8∂kit edu


  • M. Bär, B.-A. Schubert, B. Marsen, R.G. Wilks, M. Blum, S. Krause, S. Pookpanratana, Y. Zhang, T. Unold, W. Yang, L. Weinhardt, C. Heske, and H.-W. Schock, J. Mater. Res. 27, 1097 – 1104 (2012).
  • M. Bär, B.-A. Schubert, B. Marsen, S. Krause, S. Pookpanratana, T. Unold, L. Weinhardt, C. Heske, and H.-W. Schock, Appl. Phys. Lett. 99, 152111 (2011).