R. Kniese

Publications (9)12.17 Total impact

• Chapter: Bandgap Variations for Large Area Cu(In,Ga)Se2 Module Production

  R Kniese, G Voorwinden, R Menner, U Stein, M Powalla, Uwe Rau
  02/2006: pages 236-254;
• Article: Band offset at the CuGaSe2/In2S3 heterointerface

  T. Schulmeyer, A. Klein, R. Kniese, M. Powalla
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  ABSTRACT: We have investigated the electronic properties of the CuGaSe ₂/ In ₂ S ₃ heterointerface by photoelectron spectroscopy. In ₂ S ₃ was evaporated by physical vapor deposition onto contamination free polycrystalline CuGaSe ₂ surface prepared by the selenium decapping process. A valence band offset ΔE_VB=0.78±0.1 has been determined.
  Applied Physics Letters 09/2004; · 3.84 Impact Factor
• Conference Proceeding: Removal of the surface inversion of CuInSe/sub 2/ absorbers by NH/sub 3,aq./ etching

  R. Hunger, T. Schulmeyer, M. Lebedev, A. Klein, W. Jaegermann, R. Kniese, M. Powalla, K. Sakurai, S. Niki
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  ABSTRACT: The surface modifications of CIGS and CIS absorbers induced by air oxidation for 16 h, water rinsing, and diluted, 2.5 M ammonia solution, were investigated by synchrotron-excited photoelectron spectroscopy. The air oxidation leads to the outdiffusion of Na to the absorber surface under the formation of Na/sub 2/CO/sub 3/. The surface Na compounds are completely removed by water exposure. Furthermore, the air oxidation and subsequent water rinsing are accompanied by a reduction of the surface Ga concentration by a factor of 2. Ammonia etching effects the complete removal of surface oxides, a significant increase of the surface [Cu]/[In] ratio, and a removal of the initial surface inversion. These effects point towards a preferential leaching of indium out of the absorber surface.
  Photovoltaic Energy Conversion, 2003. Proceedings of 3rd World Conference on; 06/2003
• Conference Proceeding: Interface formation between polycrystalline Cu(In,Ga)Se/sub 2/ and II-VI-compounds

  T. Schulmeyer, R. Hunger, W. Jaegermann, A. Klein, R. Kniese, M. Powalla
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  ABSTRACT: The interface between Cu(In,Ga)Se/sub 2/ (absorber) and CdS (buffer) is crucial for the performance of CIGS thin film solar cells. We have performed systematic studies of interface formation between Cu(In,Ga)Se/sub 2/ and II-Vl semiconductors CdX and ZnX (X= S, Se, Te) using in-situ photoelectron spectroscopy. Clean Cu(In,Ga)Se/sub 2/ surfaces with Cu deficient surface composition were prepared by heating-off of Se layers, which were deposited onto the absorber layers in the deposition chamber directly after absorber deposition. Interfaces with II-VI compounds were prepared by stepwise evaporation. The determined band alignments are compared to theoretical calculations.
  Photovoltaic Energy Conversion, 2003. Proceedings of 3rd World Conference on; 06/2003
• Article: Highly efficient CIS solar cells and modules made by the co-evaporation process

  M. Powalla, G. Voorwinden, D. Hariskos, P. Jackson, R. Kniese
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  ABSTRACT: Thin-film photovoltaic modules which use the chalcopyrite Cu(In,Ga)(Se,S)2 (CIGS) as the light-absorbing layer have now entered the decisive industrial phase. Companies located mainly in Germany and Japan will produce more than 100 MWp CIGS modules in 2008, demonstrating that the CIGS technology has already achieved a certain maturity. Whereas key features of the technology are already well-optimized, there are several approaches to further improve the productivity of new lines. The ZSW operates a line for 30 × 30 cm2 modules in which all process steps – from glass cleaning to module encapsulation – are being developed. A major goal of the development is the very fast and efficient transfer of promising new materials and processes from cells to the industrial module level. Therefore, ZSW is focusing on processes like the in-line co-evaporation method for CIS or chemical bath deposition for buffer layers to optimize the junction. We could demonstrate efficiencies close to 18% for small test cells and 14–15% for modules with modified processes. Different cell and material data from optoelectronic measurements and microscopic analysis will be presented in this contribution.
  Thin Solid Films.
• Article: Testing of flexible Cu In,Ga Se2 based thin film solar cells in view of space applications

  C.A. Kaufmann, A. Neisser, Th. Unold, R. Klenk, H.W. Schock, F. Kessler, R. Kniese, D. Herrmann, M. Powalla, M. Kroon, G. Oomen, D Slootweg
• Article: Large-area CIGS modules: Pilot line production and new developments

  M. Powalla, M. Cemernjak, J. Eberhardt, F. Kessler, R. Kniese, H.D. Mohring, B. Dimmler
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  ABSTRACT: Thin-film solar modules based on Cu(In,Ga)Se2 (CIGS) promise to become a lower-cost alternative to polycrystalline silicon. The ZSW and Wuerth Solar are developing and running industrial processes suitable for the mass production of CIGS modules. Yield and output in the Wuerth Solar pilot line are steadily improving, with average module efficiencies exceeding 10%. New developments at the ZSW include doubling the length of the linear evaporation source to increase the throughput and adjusting the processes to enable production of flexible modules. New calculations regarding module design for optimized performance are presented as well as results from outdoor testing of Wuerth Solar modules.
  Solar Energy Materials and Solar Cells 90:3158-3164. · 4.54 Impact Factor
• Article: Influence of Cu(In,Ga)Se2 band gap on the valence band offset with CdS

  T. Schulmeyer, R. Kniese, R. Hunger, W. Jaegermann, M. Powalla, A. Klein
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  ABSTRACT: The absorber/buffer interface is essential for high-performance thin film chalcopyrite solar cells. In this contribution we present studies of interface formation between Cu(In,Ga)Se2 with 30 and 100% Ga content and the II–VI semiconductor CdS using in situ photoelectron spectroscopy. Clean Cu(In,Ga)Se2 surfaces with a Cu-deficient surface composition were prepared by heating-off of Se layers, which were deposited onto the absorber layers in the deposition chamber directly after absorber deposition. Interfaces with CdS were prepared by stepwise evaporation. The determined band alignments are compared to theoretical calculations.
  Thin Solid Films · 1.89 Impact Factor
• Article: Interfaces of chalcogenide solar cells: a study of the composition at the Cu(In,Ga)Se2/CdS contact

  T. Schulmeyer, R. Hunger, R. Fritsche, B. Jäckel, W. Jaegermann, A. Klein, R. Kniese, M. Powalla
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  ABSTRACT: The chemical composition of the Cu(In,Ga)Se2/CdS interface is studied using photoelectron spectroscopy, with monochromatized Al Kα and synchrotron radiation as excitation source. The samples were prepared by the decapping of Se layers, yielding a Cu-poor surface composition. CdS deposition and photoemission were performed in the same vacuum system. An excess of sulfur is detected at very low CdS thickness. However, reference experiments suggest that the interface is atomically abrupt. In contrast to the interface of CdS with a stoichiometric CuInSe2 single-crystal surface, the formation of CuxS at elevated temperatures is suppressed by the Cu-poor surface phase.
  Thin Solid Films · 1.89 Impact Factor