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9 results on '"Eckner S"'

2. Atomic Scale Structure of Ag,Cu 2 ZnSnSe4 and Cu2Zn Sn,Ge Se 4 Kesterite Thin Films

Author

Ritter, K., Gurieva, G., Eckner, S., Prei , C., Ritzer, M., Hages, C.J., Welter, E., Agrawal, R., Schorr, S., and Schnohr, C.S.

Subjects
Photovoltaics and Wind Energy
Abstract

Kesterite based materials are being researched and developed as affordable, efficient, and mechanically flexible absorber materials for thin film photovoltaics. Both Ag,Cu 2ZnSnSe4 and Cu2Zn Sn,Ge Se4 based devices have shown great potential in overcoming some of the remaining challenges for further increasing the conversion efficiency of kesterite based solar cells. This study therefore investigates the long range crystallographic structure and the local atomic scale structure of technologically relevant thin films by means of grazing incidence X ray diffraction and low temperature X ray absorption spectroscopy. As expected, the unit cell dimensions change about an order of magnitude more than the element specific average bond lengths. In case of Cu2Zn Sn,Ge Se4, the thin film absorbers show a very similar behavior as Cu2Zn Sn,Ge Se4 powder samples previously studied. Small amounts of residual S in the thin films were taken into account in the analysis and the results imply a preferential formation of Sn S bonds instead of Ge S bonds. In Ag,Cu 2ZnSnSe4, the dependence of the Ag Se and Cu Se bond lengths on Ag Ag Cu might indicate an energetic advantage in the formation of certain local configurations

Published
2021

5. Atomic-scale structure, cation distribution, and bandgap bowing in Cu(In,Ga)Se2 and Cu(In,Ga)S2

Author

Eckner, S., Kämmer, H., Steinbach, Tobias, Gnauck, Martin, Johannes, Andreas, Stephan, Christiane, Schorr, Susan, and Schnohr, C. S.

Subjects
ddc:530
Abstract

Applied physics letters 103, 081905 (2013). doi:10.1063/1.4819225, Mixed chalcopyrite semiconductors like Cu(In,Ga)S2 and Cu(In,Ga)Se2 are characterized by thecoexistence of different local atomic arrangements around the S or Se anion. The resulting aniondisplacement strongly influences the material bandgap. We studied the atomic-scale structure ofCu(In,Ga)S2 as a function of composition using x-ray absorption spectroscopy and valence forcefield simulations. Applying a specially developed model for not fully random cation distributions,we find that structural relaxation of the anion with respect to In and Ga contributes significantlymore to the bandgap bowing observed for Cu(In,Ga)S2 and Cu(In,Ga)Se2 than relaxation withrespect to Cu and group-III atoms., Published by American Institute of Physics, Melville, NY

Published
2013
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8. Coarsening Dynamics on $$\mathbb {Z}^d$$ with Frozen Vertices.

Author

Damron, M., Eckner, S., Kogan, H., Newman, C., and Sidoravicius, V.

Subjects
MARKOV processes, OSTWALD ripening, GEOMETRIC vertices, RANDOM variables, PERCOLATION theory
Abstract

We study Markov processes in which $$\pm 1$$ -valued random variables $$\sigma _x(t), x\in \mathbb {Z}^d$$ , update by taking the value of a majority of their nearest neighbors or else tossing a fair coin in case of a tie. In the presence of a random environment of frozen plus (resp., minus) vertices with density $$\rho ^+$$ (resp., $$\rho ^-$$ ), we study the prevalence of vertices that are (eventually) fixed plus or fixed minus or flippers (changing forever). Our main results are that, for $$\rho ^+ >0$$ and $$\rho ^- =0$$ , all sites are fixed plus, while for $$\rho ^+ >0$$ and $$\rho ^-$$ very small (compared to $$\rho ^+$$ ), the fixed minus and flippers together do not percolate. We also obtain some results for deterministic placement of frozen vertices. [ABSTRACT FROM AUTHOR]

Published
2015
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9. Atomic scale structure and bond stretching force constants in stoichiometric and off-stoichiometric kesterites.

Author

Ritter K, Gurieva G, Eckner S, Schwiddessen R, d'Acapito F, Welter E, Schorr S, and Schnohr CS

Abstract

The deviation from stoichiometry and the understanding of its consequences are key factors for the application of kesterites as solar cell absorbers. Therefore, this study investigates the local atomic structure of off-stoichiometric Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and Cu2ZnGeSe4 (CZGSe) by means of Extended X-ray Absorption Fine Structure Spectroscopy. Temperature dependent measurements yield the bond stretching force constants of all cation-anion bonds in stoichiometric CZTS and CZTSe and nearly stoichiometric CZGSe. Low temperature measurements allow high precision analysis of the influence of off-stoichiometry on the element specific average bond lengths and their variances. The overall comparison between the materials is in excellent agreement with measures like ionic/atomic radii and bond ionicities. Furthermore, the small uncertainties allow the identification of systematic trends in the Cu-Se and Zn-Se bond lengths of CZTSe and CZGSe. These trends are discussed in context of the types and concentrations of certain point defects, which gives insight into the possible local configurations and their influence on the average structural parameters. The findings complement the understanding of the effect of off-stoichiometry on the local structure of kesterites, which affects their electronic properties and thus their application for solar cells., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

Published
2023
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