Atomic-scale structure of kesterites
Mineralogy, Petrology and Geochemistry
Theoretical Condensed Matter Physics
Final Report Abstract
Photovoltaic energy conversion is a central route towards a sustainable energy supply, which constitutes one of the major global challenges of the twenty-first century. So-called kesterites, such as Cu2ZnSn(Se,S)4, are promising absorber materials for thin film solar cells, because they consist of mostly nontoxic and earth abundant elements. However, compared to other photovoltaic technologies their conversion efficiency is still limited. Secondary phases and structural defects in the material are believed to be one origin of this performance deficit. The presence of secondary phases depends on the preparation route, growth conditions and overall material composition. Suppression of structural defects and tailoring of material properties is approached by substituting certain elements, e.g. Sn by Ge or Cu by Ag. It is known from other mixed materials, though, that the local atomic arrangements often deviate from the long-range crystallographic structure, which in turn also affects the material properties. Therefore, a comprehensive set of kesterite materials was investigated in this project to study their local structure and its impact on material properties as well as compositional fluctuations and secondary phases in technologically relevant thin films. The atomic-scale structure on the subnanometer scale was determined with synchrotron- based X-ray absorption spectroscopy. The element-specific bond lengths are found to be distinctly different for the different cation-anion pairs, even if the elements share the same lattice sites. As a consequence, the anion position strongly depends on the type of neighbouring cations and is different for different local configurations present in the material. Theoretical calculations reveal a pronounced impact of these structural variations on the bandgap energy, which is one of the central material properties for solar cell application. Secondary phases and compositional fluctuations in kesterite thin films were studied with spatially resolved X-ray fluorescence analysis using a highly focused synchrotron nanobeam combined with different electron microscopy techniques. Depending on the preparation route and overall material composition, the presence of secondary phase segregations was observed on a submicrometer scale. Other inhomogeneities include kesterite domains and grain boundaries with varying local composition. For a different preparation route, however, the growth of homogeneous kesterite thin films without secondary phases or compositional fluctuations was shown. The results of this project thus provide unique and valuable insight into the fundamental relationship between composition, structure and properties of complex kesterite materials on a micrometer to subnanometer scale and point out optimized preparation routes in the quest for sustainable, high-efficiency thin film solar cells.
Publications
- Insights into interface and bulk defects in a high efficiency kesterite-based device, Energy Environ. Sci. 14, 507 (2021)
R. Fonoll-Rubio, J. Andrade-Arvizu, J. Blanco-Portals, I. Becerril-Romero, M. Guc, E. Saucedo, F. Peiro, L. Calvo-Barrio, M. Ritzer, C. S. Schnohr, M. Placidi, S. Estrade, V. Izquierdo-Roca, A. Perez-Rodriguez
(See online at https://doi.org/10.1039/D0EE02004D) - Discrepancy between integral and local composition in offstoichiometric Cu2ZnSnSe4 kesterites: A pitfall for classification, Appl. Phys. Lett. 110, 043901 (2017)
P. Schöppe, G. Gurieva, S. Giraldo, G. Martínez-Criado, C. Ronning, E. Saucedo, S. Schorr, C. S. Schnohr
(See online at https://doi.org/10.1063/1.4974819) - Atomic scale structure and its impact on the band gap energy for Cu2Zn(Sn,Ge)Se4 kesterite alloys, J. Phys.: Energy 2, 035004 (2020)
K. Ritter, S. Eckner, C. Preiß, G. Gurieva, T. Bischoff, E. Welter, S. Botti, S. Schorr, C. S. Schnohr
(See online at https://doi.org/10.1088/2515-7655/ab9d8b) - Interplay of performance-limiting nanoscale features in Cu2ZnSn(S,Se)4 solar cells, Phys. Stat. Sol. A 217, 2000456 (2020)
M. Ritzer, S. Schönherr, P. Schöppe, G. Larramona, C. Choné, G. Gurieva, A. Johannes, K. Ritter, G. Martínez-Criado, S. Schorr, C. Ronning, C. S. Schnohr
(See online at https://doi.org/10.1002/pssa.202000456) - On the germanium incorporation in Cu2ZnSnSe4 kesterite solar cells boosting their efficiency, ACS Appl. Energy Mater. 3, 558 (2020)
M. Ritzer, S. Schönherr, P. Schöppe, W. Wisniewski, S. Giraldo, G. Gurieva, A. Johannes, C. T. Plass, K. Ritter, G. Martínez-Criado, S. Schorr, E. Saucedo, C. Ronning, C. S. Schnohr
(See online at https://doi.org/10.1021/acsaem.9b01784) - Atomic scale structure of (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 kesterite thin films, Front. Energy Res. 9, 656006 (2021)
K. Ritter, G. Gurieva, S. Eckner, C. Preiß, M. Ritzer, C. J. Hages, E. Welter, R. Agrawal, S. Schorr, C. S. Schnohr
(See online at https://doi.org/10.3389/fenrg.2021.656006)
