Berlin 2015 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 10: Photovoltaics: Kesterites and less widely used materials (with DF)
HL 10.2: Vortrag
Montag, 16. März 2015, 11:30–11:45, ER 164
Formation of Single-Phase Cu2ZnSnS4 Thin Films by Control of Secondary Phases in a Solid State Reaction — •Justus Just1,2, Jan-Christoph Hebig1,2, Roland Mainz1, Dirk Lützenkirchen-Hecht2, Ronald Frahm2, and Thomas Unold1 — 1Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany — 2Bergische Universität Wuppertal, Gaußstraße 20, 42109 Wuppertal, Germany
The conversion efficiency of Cu2ZnSnS4(CZTS) based solar cells significantly depends on deposition conditions and specifically the composition of the material. Although best material qualities are observed for Cu-poor and Zn-rich conditions, it has been shown that the compositional region of single phase CZTS is rather small, inevitably leading to a segregation of secondary phases, especially ZnS for Zn-rich material. To overcome this, but still maintain Cu-poor and Zn-rich growth we have developed a two stage co-evaporation process including a thermal treatment. In this process CZTS is formed by a cation interdiffusion process during a solid state reaction of ZnS with ternary Cu2SnS3. By oversupplying ZnS the chemical potential of Zn is higher than needed for stoichiometric CZTS, while an uncontrolled segregation of ZnS within the CZTS layer is avoided. This method allows the synthesis of single phase CZTS as shown by X-ray absorption spectroscopy. The final absorber layers show a homogenous distribution of atoms indicating that the solid state reaction is fully completed. To investigate the diffusion kinetics as well as the recrystallization mechanism in-situ real-time X-ray diffraction measurements were performed.