The Materials

The compounds Cu(In,Ga)(S,Se)2 and Cu2ZnSn(S,Se)4 have attracted much attention as semiconductors especially due to their absorption coefficients for visible light exceeding that of crystalline silicon by two orders of magnitude. As a consequence an absorber layer of below two micrometers is already sufficient to absorb most of the incident solar power and so-called Thin Film Solar Cells become feasible. The decrease of the thickness of the absorber layer will save raw materials as well as energy input in the production process.

State of the Art

The compounds CuInSe2, CuGaSe2 and Cu(In,Ga)Se2 among other ternary compounds have shown good photovoltaic properties. First investigations of solar cell devices based on these materials have started 35 years ago. Meanwhile Cu(In,Ga)Se2 thin film solar cells are subject to active research all over the world. Although first manufactures are already producing and selling photovoltaic modules based on this technology there is still necessity for further research to clarify and to understand further material properties.

Cu2ZnSn(S,Se)4 thin films are another of the most promising materials for low-cost thin film solar cells and subject of increasing research. Compared with Cu(In,Ga)(S,Se)2 solar cells the knowledge about formation reactions, material properties and film growth is still insufficient and needs ongoing systematic investigations to enhance conversion efficiency and enable industrial fabrication.

Our Contribution (Publications)

The Thin Film Photovoltaics group focuses on investigations of Cu(In,Ga)(S,Se)2 , Cu2ZnSn(S,Se)4 and related materials by x-ray powder diffraction. We have developed a special experimental set-up which enables the detection of the semiconductor formation reactions in real time. Advanced data evaluation facilitates to determine chemical reaction equations of the synthesis of the absorber material. The experimental work is accompanied by theoretical input of thermodynamic as well as crystallographic data. These studies provide an overview on beneficial reaction paths for different chalcopyrite compounds in the phase field Cu(Al,Ga,In)(S,Se)2 and Cu2ZnSn(S,Se)4, which allows a further optimisation of the semiconductor production process. We collaborate with the Chair for Materials for Electronics and Energy Technology of the Materials Science Department (University of Erlangen-Nürnberg) and one industrial partner.