The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study |
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Authors: | Susan Schorr |
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Affiliation: | Free University Berlin, Institute of Geological Sciences, Malteserstr. 74-100, Berlin, Germany |
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Abstract: | The atomic structure of the potential photovoltaic materials Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) is discussed on the basis of a structural analysis of neutron powder diffraction data refined by the Rietveld analysis. Both compounds were found to crystallize in the kesterite type structure, but with a disorder within the Cu-Zn layers at z=1/4 and 3/4. The latter causes CuZn and ZnCu anti-site defects, whose concentration depends on the sample growth conditions.The temperature dependent structural phase transition in CZTS was studied by in-situ high temperature diffraction experiments using high energy synchrotron X-rays. The transition from the tetragonal kesterite to the cubic sphalerite type structure is discussed by means of the interplay of increasing and decreasing cation-anion-cation bond angles in the coordination tetrahedra, reflected by the shift of the anion atomic coordinates to more ideal (x and y) or non-ideal (z) values. This striking behavior may be connected with frustrations that occur due to the triangular geometry of the coordination tetrahedra. |
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Keywords: | Kesterites Thin film solar cells Compound semiconductors Crystal structure Structural phase transitions |
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