Abstract
Kesterite based materials gain more and more relevance in the pursuit of affordable, efficient and flexible absorber materials for thin film photovoltaics. Alloying Cu2ZnSnSe4 with Ge could allow controlled band gap engineering as already established for Cu(In,Ga)(S,Se)2 based solar cells. This study investigates the local atomic arrangements of Cu2Zn(Sn,Ge)Se4 alloys by means of low temperature Extended x-ray Absorbtion Fine Structure Spectroscopy. The element specific bond lengths are used together with x-ray diffraction data to derive the anion positions of the different local configurations. Ab initio theoretical calculations are performed to predict the influence of structural parameters such as anion position and lattice constants on the band gap energy. Combining the results of the experimental and theoretical studies suggests that the overall influence of the structural changes on the band gap bowing due to alloying is significant yet smaller than the total non-linear change of the band gap energy. Consequently, it is concluded, that band gap bowing stems from both structural and electronic changes.
Highlights
July 2020Original Content from this work may be used under the terms of the Creative Commons
Cu2ZnSnS4 and Cu2ZnSnSe4, typically referred to as kesterites, are well investigated quaternary semiconductors
This study investigates the local atomic arrangements of Cu2Zn(Sn,Ge)Se4 alloys by means of low temperature Extended x-ray Absorbtion Fine Structure Spectroscopy
Summary
Original Content from this work may be used under the terms of the Creative Commons. Max-Wien-Platz 1, 07743 Jena, Germany 4 Chaire de Simulationa l’Echelle Atomique, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland 5 Deutsches Elektronen-Synchrotron DESY - A Research Centre of the Helmholtz Association, 22607 Hamburg, Germany 6 Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany 7 Institut für Geologische Wissenschaften, Freie Universitat Berlin, Malteserstr. 74-100, 12249 Berlin, Germany 8 Author to whom any correspondence should be addressed.
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