Carola Klimm
Helmholtz-Zentrum Berlin
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Publication
Featured researches published by Carola Klimm.
Journal of Applied Physics | 2011
Tobias Sontheimer; Simone Scherf; Carola Klimm; Christiane Becker; Bernd Rech
The kinetics of crystal nucleation in high-rate electron beam evaporated amorphous Si for polycrystalline thin film solar cells was systematically studied on SiN and selected ZnO:Al-coated glass substrates with dissimilar surface topographies by employing Raman spectroscopy, transmission electron microscopy, and optical microscopy. The influence of the surface topography of the substrate and the disorder of the deposited amorphous Si could be correlated to the respective characteristics of the transient and steady state regime of the nucleation rate. The steady state nucleation rate Iss, its corresponding activation energy EIss, and consequently the size of the grains in the crystallized Si were found to be governed by the interplay between the surface roughness and the deposition temperature. The steady state nucleation rate Iss increased gradually upon increasing the substrate roughness, while lowering the deposition temperature of the amorphous Si on rough textures resulted in a decline of Iss. The tim...
photovoltaic specialists conference | 2010
Tobias Sontheimer; Christiane Becker; Florian Ruske; Carola Klimm; U. Bloeck; S. Gall; O. Kunz; T. Young; R. Egan; J. Hüpkes; Bernd Rech
Electron-beam (e-beam) evaporation provides both exciting opportunities and challenges for the preparation of poly-crystalline silicon (poly-Si) thin film solar cells. A conversion efficiency of 6.7% was recently achieved for solid phase crystallized poly-Si mini-modules on planar SiN-coated glass deposited at a deposition rate of 600 nm/min, demonstrating the excellent electronic quality of e-beam evaporated silicon. Even at significantly increased background pressures of 5×10−6 mbar, the photovoltaic performance of the mini-modules was considerably high, showing a decline in open circuit voltage of 17 mV per cell. The implementation of light trapping structures into the device led to an efficiency increase of 1.1%, yielding module efficiencies of 7.8%. By systematically studying the implementation of ZnO:Al as a front contact layer into the poly-Si solar cell device structure, we unraveled novel features that prove the supreme suitability of ZnO:Al for poly-Si thin film solar cells. Not only can etched ZnO:Al be utilized as a front side texture, but its electrical properties can also improve during the crystallization process of the Si layer, showing a record charge carrier mobility of 67 cm2/Vs after thermal annealing. In addition, ZnO:Al drastically modifies the crystallization kinetics of the Si on ZnO:Al, enabling us to control the crystallization process by adjusting the deposition temperature. The nucleation process of Si on ZnO:Al was found to be influenced by a variation of the deposition temperature of the amorphous Si in a critical temperature regime of 200 °C to 300 °C. The nucleation rate decreased significantly with decreasing deposition temperature, while the activation energy for nucleation increased from 2.9 eV at a deposition temperature of 300 °C to 5.1 eV at 200 °C, resulting in poly-Si which comprised grains with features sizes of several µm.
Applied Physics Letters | 2013
Sven Käbisch; Marc A. Gluba; Carola Klimm; Stefan Krause; Norbert Koch; N. H. Nickel
Catalyst-free ZnO nanostructures were grown by pulsed-laser deposition on c-oriented sapphire. The nanostructure morphology can be controlled by introducing a nucleation layer. Depending on the doping concentration in the nucleation layer two distinct types of nanostructures are observed. On intrinsic nucleation layers nanowires form, while Al-doping results in a honeycomb network of nanoscale walls. From scanning-electron microscopy and X-ray photoelectron spectroscopy a correlation between nanostructure morphology and the polarity of the nucleation layers is derived.
Applied Physics Letters | 2012
M. Weizman; Carola Klimm; N. H. Nickel; Bernd Rech
The origin of the formation of {100} and {111} grain textures in polycrystalline silicon thin films prepared with multiple excimer laser shots at the super-lateral-growth crystallization regime is investigated in this study. Our results demonstrate that the type of texture formed is determined solely by the thickness of the silicon layer. At a critical value of 40 nm, a transition from {100} to {111} texture is observed with increasing layer thickness. It is therefore proposed that below this critical value, the texture formation is governed by surface energy anisotropy whereas above it, the kinetics of the solidification process predominate.
Solid State Phenomena | 2012
Heike Angermann; Uta Stürzebecher; Jan Kegel; Christiane Gottschalk; Klaus Wolke; A. Laades; E. Conrad; Carola Klimm; Bert Stegemann
For further enhancement of solar energy conversion efficiency the passivation of silicon (Si) substrate surfaces and interfaces of Si-based solar cell devices is a decisive precondition to reduce recombination losses of photogenerated charge carriers. These losses are mainly controlled by surface charges, the density and the character of rechargeable interface states (Dit) [], which are induced by defects localised in a small interlayer extending over only few Å. Therefore, the application of fast non-destructive methods for characterization of the electronic interface properties directly during the technological process has received an increasing interest in recent years.
Solid State Phenomena | 2009
W. Sievert; K.U. Zimmermann; B. Hartmann; Carola Klimm; K. Jacob; Heike Angermann
Continuously increasing prices for energy and general environmental concerns over the past few years have lead to an enormous growth of interest in alternative forms of energy and solar energy in specific. According to industry experts the manufacturing focus of the photovoltaic industry will be on silicon for at least another 5 to 10 years. The development of economically attractive silicon solar cells appropriates interface preparation and passivation methods to optimize the light trapping properties and to reduce recombination losses on structured interfaces [1]. The texturization of Si substrates, however, leads to a strong increase in crystallographic surface irregularities, resulting in a high density of rechargeable states and in high recombination losses on structured interfaces [2]. To reduce the density of these states, it is necessary to remove the damaged surface layer and to decrease the micro-roughness of structured surfaces on the nanometer scale.
Solid State Phenomena | 2012
Heike Angermann; A. Laades; Uta Stürzebecher; E. Conrad; Carola Klimm; Tim F. Schulze; K. Jacob; Alexander Lawerenz; Lars Korte
The dominance of crystalline silicon (Si) in photovoltaics can be ascribed partly to the extensive knowledge about this material, which has been accumulated in microelectronics technology. Methods to passivate Si interfaces, which were developed for microelectronic device technologies, have been extended to solar cell manufacturing in the past. These methods, however, have been optimised for polished substrates, and do not work so effective with textured surfaces, which commonly used in the fabrication of high efficiency Si solar cells to enhance anti-reflection properties.
photovoltaic specialists conference | 2013
Sebastian S. Schmidt; Christian Wolf; Niklas Papathanasiou; Rutger Schlatmann; Carola Klimm; M. Klaus; Christoph Genzel; Maik Billing; Hans-Werner Schock
Cu(In, Ga)Se2 solar cell absorbers are prepared on a Mo-coated glass substrate by using a sequential process consisting of a sputter deposition of an In/CuGa/In metal precursor, subsequent PVD deposition of a Se layer and annealing in N2 atmosphere. The Se concentration in the final layer stack was found to be relatively up to 20 % higher than expected. The excess Se is bound in a MoSe2 layer with laterally varying thickness, between the absorber and the Mo back contact. Such a layer can lead to an increase in the series resistance of the completed solar cells. By pumping at a specific time, we were able to reduce the Se partial pressure selectively during the selenization. For a constant annealing time, we find that the MoSe2 thickness increases with the time in which a high Se partial pressure is maintained, i.e., the time before the selective pumping. A significant reduction of the Se partial pressure after half the annealing time led to solar cells with the smallest series resistance and overall best conversion efficiency. We further found that the addition of NaF before the annealing led to comparatively thin MoSe2 layers. This suggests that the Na incorporation from the glass substrate in our process is too small to hinder the MoSe2 growth. A more specific control of the Na supply is required in our process to manipulate the MoSe2 growth and the doping density in the absorber.
international vacuum electron sources conference | 2014
Roman Barday; Andreas Jankowiak; T. Kamps; Carola Klimm; Jens Knobloch; Frank Siewert; A. Varykhalov; Boris Senkovskiy; S. Lagotzky; G. Muller
Molybdenum is widely used in fundamental research and industry, for example as substrate for photocathodes or electrode material in DC photoelectron guns. Usually, Mo is heated in situ to several hundred degrees to achieve an oxygen free surface for the photocathode deposition or to reduce the surface outgassing rate in the electron gun. Since enhanced field emission (EFE) is often observed there, we have investigated the influence of oxides on the EFE of Mo by means of a field emission scanning microscope (FESM) and x-ray photoelectron spectroscopy (XPS).
Solar Energy Materials and Solar Cells | 2013
Christiane Becker; Daniel Amkreutz; Tobias Sontheimer; Veit Preidel; Daniel Lockau; Jan Haschke; Lisa Jogschies; Carola Klimm; Janis Merkel; Paul Plocica; Simon Steffens; Bernd Rech