Key Publications

Andreas Stoffers, Oana Cojocaru-Mirédin, Winfried Seifert, Stefan Zaefferer, Stephan Riepe, and Dierk Raabe, "Grain boundary segregation in multicrystalline silicon: correlative characterization by EBSD, EBIC, and atom probe tomography," Progress in Photovoltaics: Research and Applications 23 (12), 1742-1753 (2015).
Oana Cojocaru-Mirédin, Yanpeng Fu, Aleksander Kostka, Rodrigo Sáez-Araoz, Andreas Beyer, Nikolai Knaub, Kerstin Volz, Christian-Herbert Fischer, and Dierk Raabe, "Interface engineering and characterization at the atomic-scale of pure and mixed ion layer gas reaction buffer layers in chalcopyrite thin-film solar cells," Progress in Photovoltaics: Research and Applications 23 (6), 705-716 (2015).
O. Cojocaru-Mirédin, T. Schwarz, P. Choi, M. Herbig, R. Würz, and D. Raabe, "Atom Probe Tomography Studies on the Cu(In,Ga)Se2 Grain Boundaries," Journal of Visualized Experiments 74, e50376 (2013).
P. Choi, O. Cojocaru-Mirédin, D. Abou-Ras, R. Caballero, D. Raabe, V. Smentkowski, C. G. Park, G. H. Gu, B. Mazumder, M. H. Wong, Y.-L. Hu, T. P. Melo, and J. S. Speck, "Atom-Probe Tomography of compound semiconductors for photovoltaic and light-emitting device applications," Microscopy Today 20 (3), 18-24 (2012).
O. Cojocaru-Mirédin, P. Choi, R. Wuerz, and D. Raabe, "Exploring the p-n junction region in Cu(In,Ga)Se2 thin-film solar cells at the nanometer-scale," Applied Physics Letters 101 (18), 181603-1-181603-5 (2012).

Funded by

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Nanocharacterization for Advanced Functional Materials

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Nanocharacterization for Advanced Functional Materials
        "Cooperation with RWTH Aachen University"

The goal of this research group is to understand the relationship between the chemical, electrical, and structural properties for a series of interface-dominated solar cells (multicrystalline Si and thin-film solar cells). This is achieved by performing correlative studies on specific regions using joint electron backscatter diffraction/transmission electron microsocpe, electron beam-induced current/cathodoluminescence, and atom probe tomography.

Group Mission

This group is supported essentially by the “Federal Ministry of Education and Research” (Bundesministerium für Bildung und Forschung, BMBF). The mission of this group is to optimize the solar cells efficiency based on the 3D chemical analysis at the atomic-scale.
This research group is focused on multicrystalline silicon (m-Si) solar cell, and Cu2ZnSnSe4 (CZTS) and Cu(In,Ga)Se2 (CIGS) thin-film solar cells, which are already commercially available because of their relatively high efficiency compared with their counterparts. To further establish the bulk and thin-film technologies, both the reduction of the production costs and the enhancement of solar cell efficiency are essential.
The atomic redistribution of the impurities at the internal interfaces (grain boundaries and p-n junction) may affect the efficiency of a solar cell. For example, the figure below illustrates that the efficiency of a CIGS solar cell had been improved with almost 50% only by adding a very few amount of Na atoms (~ 0.1 at.%) inside the absorber layer. Furthermore, Fig.1 indicates that this increase in the efficiency can be directly correlated with the Na segregation at the CIGS grain-boundaries.

Correlation between Processing/Microstructure, Efficiency, and Atomic Distribution in Cu(In,Ga)Se2 - thin film solar cells. Zoom Image

Correlation between Processing/Microstructure, Efficiency, and Atomic Distribution in Cu(In,Ga)Se2 - thin film solar cells.


In conclusion, the goal of this research group is to understand the relationship between the microstructure, efficiency and atomic redistribution for a series of interface-dominated solar cells.

Research Highlight 2009-2015

Since more than four years, we work on different thin-film solar cells using a very new and powerful technique called atom probe tomography (APT), a technique which is expected to have a great contribution to solar cells development. The aim is to characterize the redistribution of the elements and impurities within the internal interfaces and planar defects and to correlate these chemical properties with the electrical and structural ones. This work is in close collaboration with famous research institutes in solar technology such as Zentrum für Sonnenenergie – und Wasserstoff Forschung Baden-Württemberg (ZSW-Stuttgart) and Helmholz Zentrum Berlin (HZB), Luxembourg University, Lyon University, Cottbus University, MPI Halle, etc.

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