Prof. Ralf B. Wehrspohn Profile

Prof. Ralf B. Wehrspohn

at Fraunhofer Institute of IMWS

SPIE Involvement:

Editor | Author

Publications (33)

Proceedings Article | 23 May 2018 Presentation

Strategy for tailoring nanospheres for rough interfaces in solar cells (Conference Presentation)

Stefan Nanz, Aimi Abass, Peter Piechulla, Alexander Sprafke, Ralf Wehrspohn, Carsten Rockstuhl

Proc. SPIE. 10688, Photonics for Solar Energy Systems VII

KEYWORDS: Thin films, Diffraction, Scattering, Solar cells, Crystals, Interfaces, Silicon, Light scattering, Thin film solar cells, Crystallography

Read Abstract +

The availability of optimum textures for the purpose of light trapping in solar cells is at stake. Here, we discuss how they can be obtained with a large-area scalable bottom-up approach that utilizes as a template monolayers of densely packed nanospheres from a colloidal solution with tailored size distribution. Theoretically, we show that the surface textures' geometry can be predicted and tuned from a colloidal solution with given nanosphere sizes and relative occurrence probability. With only simple monolayers comprised of two nanosphere size species, we show that one can already obtain a useful scattering pattern relevant for rear scattering light trapping textures. We proceeded to study the application of such textures in thin-film crystalline silicon (c-Si) solar cells. Such monolayers can be tuned to provide diffraction patterns, which form an annulus in Fourier space such that stronger scattering occurs at oblique angles. For such two species nanosphere monolayers, the nanosphere sizes dominantly influence the diffraction efficiency and minimum and maximum scattering angles. The relative occurrence probability of each nanopshere species influences the amount of diffraction states accessible, which translates to how broad the annulus region in Fourier space can be. The simplicity of the monolayer and the behavior of the scattering response allows to easily estimate nanosphere size ranges of interest by considering the radiation condition in c-Si and in air. In optimizing the monolayer parameters to obtain optimum rear scattering light trapping textures, we inspect approaches that avoid the severe computational costs, which typically follow the modeling of random scattering geometries. In particular, we investigate the applicability of utilizing the surface texture's Power Spectral Density (PSD) and alternatively rigorous diffraction calculations in a semi-infinite c-Si superstrate to deduce net short-circuit current enhancement dependence on the monolayer parameters. The widely used PSD based prediction is shown to significantly deviate in important parameter ranges, where an optimal response can be obtained. This is related to the limitation of the PSD to be used as a predictor for the scattering response at textures with a notable height modulation. In the regime where the PSD fails to be predictive, an excellent prediction on the short-circuit current enhancement can be obtained with minimal computational costs by only examining the diffraction efficiencies in a selected wavelength range where light trapping has its largest impact. We show that the integrated diffraction in the directions of interest at the wavelength of 700 nm is sufficiently representative for the considered 1 μm thin-film c-Si cell and light trapping scheme. Fullwave simulations reveal that the integrated diffraction at 700 nm and the short-circuit current have coinciding trends in their dependency on the nanosphere size distribution. We furthermore explore the usage of the nanosphere monolayer template to obtain front surface textures, which provide mainly anti-reflection properties. This is done by considering an inverse pattern of the template to make use of the needle-like structures that emerge from the inverted nanosphere monolayer. The conditions needed for the monolayer parameters in order to ensure broadband suppression of reflection are discussed.

Proceedings Article | 29 April 2016 Paper

Enhanced density of negative fixed charges in Al2O3 layers on Si through a subsequent deposition of TiO2

Thomas Schneider, Johannes Ziegler, Kai Kaufmann, Klemens Ilse, Alexander Sprafke, Ralf Wehrspohn

Proc. SPIE. 9898, Photonics for Solar Energy Systems VI

KEYWORDS: Oxides, Titanium dioxide, Etching, Crystals, Dielectrics, Interfaces, Silicon, Diffusion, Quality measurement, Silicon solar cells, Atomic layer deposition, Aluminum, Chlorine, Corundum

Read Abstract +

Proceedings Article | 16 September 2013 Paper

Nanowires from dirty multi-crystalline Si for hydrogen generation

Xiaopeng Li, Stefan Schweizer, Alexander Sprafke, Ralf Wehrspohn

Proc. SPIE. 8822, Solar Hydrogen and Nanotechnology VIII

KEYWORDS: Etching, Metals, Silicon, Hydrogen, Reflectivity, Scanning electron microscopy, Chemical elements, Semiconducting wafers, Absorption, Nanowires

Read Abstract +

Proceedings Article | 11 September 2013 Paper

3D photonic crystals for photon management in solar cells

S. Schweizer, A. Sprafke, R. Wehrspohn

Proc. SPIE. 8808, Active Photonic Materials V

KEYWORDS: Thin films, Diffraction, Solar energy, External quantum efficiency, Reflection, Solar cells, Crystals, Silicon, Photonic crystals, Diffraction gratings

Read Abstract +

Proceedings Article | 2 May 2012 Paper

Black silicon for solar cell applications

Matthias Kroll, Martin Otto, Thomas Käsebier, Kevin Füchsel, Ralf Wehrspohn, Ernst-Bernhard Kley, Andreas Tünnermann, Thomas Pertsch

Proc. SPIE. 8438, Photonics for Solar Energy Systems IV

KEYWORDS: Nanostructures, Antireflective coatings, Etching, Solar cells, Dielectrics, Interfaces, Silicon, Optical coatings, Reflectivity, Absorption

Read Abstract +

Proceedings Article | 2 May 2012 Paper

Black silicon photovoltaics

Kevin Füchsel, Matthias Kroll, Thomas Käsebier, Martin Otto, Thomas Pertsch, Ernst-Bernhard Kley, Ralf Wehrspohn, Norbert Kaiser, Andreas Tünnermann

Proc. SPIE. 8438, Photonics for Solar Energy Systems IV

KEYWORDS: Oxides, Nanostructuring, Etching, Solar cells, Interfaces, Silicon, Reflectivity, Silicon films, Transparent conductors, Nanolithography

Read Abstract +

Proceedings Article | 12 September 2011 Paper

Periodic silicon nanostructures for spectroscopic microsensors

Ralf Wehrspohn, Benjamin Gesemann, Daniel Pergande, Torsten Geppert, Stefan Schweizer, Susanne Moretton, Armin Lambrecht

Proc. SPIE. 8095, Active Photonic Materials IV

KEYWORDS: Gas sensors, Carbon dioxide, Sensors, Etching, Silicon, Photonic crystals, Platinum, Ionization, Infrared radiation, Absorption

Read Abstract +

Proceedings Article | 11 September 2010 Paper

3D photonic crystals for photon management in solar cells

J. Üpping, A. Bielawny, C. Ulbrich, M. Peters, J. Goldschmidt, L. Steidl, R. Zentel, T. Beckers, A. Lambertz, R. Carius, U. Rau, R. Wehrspohn

Proc. SPIE. 7756, Active Photonic Materials III

KEYWORDS: Reflectors, Solar concentrators, External quantum efficiency, Optical spheres, Reflection, Solar cells, Crystals, Photonic crystals, Zinc oxide, Absorption

Read Abstract +

Proceedings Article | 18 May 2010 Paper

Optical characterization of 3D photonic structures for light trapping in crystalline silicon solar cells

Sebastian Knabe, Sebastian Wilken, Johannes Üpping, Ralf Wehrspohn, Gottfried Bauer

Proc. SPIE. 7725, Photonics for Solar Energy Systems III

KEYWORDS: Optical filters, Optical spheres, Reflection, Glasses, Luminescence, Photons, Crystals, Silicon, Photonic crystals, Semiconducting wafers

Read Abstract +

Proceedings Article | 18 May 2010 Paper

Inverted-opal photonic crystals for ultra light-trapping in solar cells

J. Üpping, C. Ulbrich, C.. Helgert, M. Peters, L. Steidl, R. Zentel, T. Pertsch, U. Rau, R. Wehrspohn

Proc. SPIE. 7725, Photonics for Solar Energy Systems III

KEYWORDS: Optical filters, Solar energy, Optical spheres, Sun, Reflection, Solar cells, Crystals, Quantum efficiency, Photonic crystals, Absorption

Read Abstract +

Proceedings Article | 18 May 2010 Paper

Micromorph silicon tandem solar cells with fully integrated 3D photonic crystal intermediate reflectors

J. Üpping, A. Bielawny, S. Fahr, C. Rockstuhl, F. Lederer, L. Steidl, R. Zentel, T. Beckers, A. Lambertz, R. Carius, R. Wehrspohn

Proc. SPIE. 7725, Photonics for Solar Energy Systems III

KEYWORDS: Reflectors, Thin films, External quantum efficiency, Crystals, Silicon, Reflectivity, Photonic crystals, Atomic layer deposition, Zinc oxide, Tandem solar cells

Read Abstract +

Proceedings Article | 18 May 2010 Paper

Optical modeling of needle like silicon surfaces produced by an ICP-RIE process

Matthias Kroll, Thomas Käsebier, Martin Otto, Roland Salzer, Ralf Wehrspohn, Ernst-Bernhard Kley, Andreas Tünnermann, Thomas Pertsch

Proc. SPIE. 7725, Photonics for Solar Energy Systems III

KEYWORDS: Reflection, Scattering, Etching, Silicon, Light scattering, Reflectivity, Reactive ion etching, Semiconducting wafers, Surface finishing, Absorption

Read Abstract +

Proceedings Article | 18 May 2010 Paper

Strain dependence of second-harmonic generation in silicon

Clemens Schriever, Christian Bohley, Jörg Schilling, Ralf Wehrspohn

Proc. SPIE. 7719, Silicon Photonics and Photonic Integrated Circuits II

KEYWORDS: Oxides, Second-harmonic generation, Reflection, Crystals, Interfaces, Silicon, Nonlinear optics, Signal generators, Harmonic generation, Nonlinear crystals

Read Abstract +

Proceedings Article | 2 September 2009 Paper

Infiltration of individual pores in macroporous silicon photonic crystals

Peter Nolte, Daniel Pergande, Stefan Schweizer, Markus Geuss, Roland Salzer, Brian Makowski, Martin Steinhart, Ralf Wehrspohn, Christoph Weder

Proc. SPIE. 7393, Nanophotonic Materials VI

KEYWORDS: Fabrication, Gold, Polishing, Polymers, Crystals, Silicon, Photonic crystals, Ion beams, Nonlinear optics, Silicon photonics

Read Abstract +

Proceedings Article | 21 August 2009 Paper

Electric transport in 3D photonic crystal intermediate reflectors for micromorph thin-film tandem solar cells

J. Üpping, A. Bielawny, S. Lee, M. Knez, R. Carius, R. Wehrspohn

Proc. SPIE. 7409, Thin Film Solar Technology

KEYWORDS: Reflectors, Thin films, External quantum efficiency, Reflectivity, Photonic crystals, Atomic layer deposition, Zinc oxide, Prototyping, Tandem solar cells, Absorption

Read Abstract +

Proceedings Article | 19 May 2009 Paper

Fast transient temperature operating micromachined emitter for mid-infrared for optical gas sensing systems

J. Hildenbrand, C. Peter, F. Lamprecht, A. Kürzinger, F. Naumann, M. Ebert, R. Wehrspohn, J. Wöllenstein

Proc. SPIE. 7362, Smart Sensors, Actuators, and MEMS IV

KEYWORDS: Modulation, Etching, Silicon, Resistance, Platinum, Photoresist materials, Aluminum, Reactive ion etching, Semiconducting wafers, Temperature metrology

Read Abstract +

Proceedings Article | 8 May 2008 Paper

Directional selectivity and light-trapping in solar cells

Carolin Ulbrich, Stephan Fahr, Marius Peters, Johannes Üpping, Thomas Kirchartz, Carsten Rockstuhl, Jan Christoph Goldschmidt, Philipp Löper, Ralf Wehrspohn, Andreas Gombert, Falk Lederer, Uwe Rau

Proc. SPIE. 7002, Photonics for Solar Energy Systems II

KEYWORDS: Energy efficiency, Optical filters, Solar energy, External quantum efficiency, Sun, Solar cells, Diffusion, Quantum efficiency, Optical coatings, Silicon solar cells

Read Abstract +

Proceedings Article | 5 May 2008 Paper

Three-dimensional photonic crystals as intermediate filter for thin-film tandem solar cells

Andreas Bielawny, Paul Miclea, Ralf Wehrspohn, Seung-Mo Lee, Mato Knez, Carsten Rockstuhl, Marian Lisca, Falk Lederer, Reinhard Carius

Proc. SPIE. 7002, Photonics for Solar Energy Systems II

KEYWORDS: Amorphous silicon, Thin films, Optical spheres, Solar cells, Crystals, Composites, Silicon, Reflectivity, Photonic crystals, Zinc oxide

Read Abstract +

Proceedings Article | 5 May 2008 Paper

3D photonic crystals for ultra-light trapping in solar cells

J. Üpping, A. Bielawny, P. Miclea, R. Wehrspohn

Proc. SPIE. 7002, Photonics for Solar Energy Systems II

KEYWORDS: Solar energy, External quantum efficiency, Optical spheres, Sun, Solar cells, Crystals, Photonic crystals, Zinc oxide, Microwave radiation, Correlation function

Read Abstract +

Proceedings Article | 21 April 2008 Paper

Thermal emission properties of 2D and 3D silicon photonic crystals

Benjamin Gesemann, Stefan Schweizer, Ralf Wehrspohn

Proc. SPIE. 6989, Photonic Crystal Materials and Devices VIII

KEYWORDS: Oxides, Modulation, Crystals, Tungsten, Silicon, Photonic crystals, Numerical simulations, 3D metrology, Silicon photonics, Temperature metrology

Read Abstract +

Proceedings Article | 11 September 2007 Paper

Diffractive and energy selective photonic crystals for thin-film tandem solar cells

Andreas Bielawny, Paul Miclea, Ralf Wehrspohn, Andreas von Rhein, Carsten Rockstuhl, Marian Lisca, Falk Lederer, Birger Lange, Rudolf Zentel, Reinhard Carius

Proc. SPIE. 6651, Photovoltaic Cell and Module Technologies

KEYWORDS: Thin films, Diffraction, Optical spheres, Photons, Crystals, Silicon, Photonic crystals, Thin film solar cells, Tandem solar cells, Absorption

Read Abstract +

Proceedings Article | 7 March 2007 Paper

Silicon-based low-loss photonic crystal waveguides

Daniel Pergande, Alexey Milenin, Torsten Geppert, Andreas von Rhein, Ralf Wehrspohn

Proc. SPIE. 6475, Integrated Optics: Devices, Materials, and Technologies XI

KEYWORDS: Silica, Waveguides, Etching, Silicon, Reflectivity, Photonic crystals, Chromium, Photomasks, Silicon photonics, Semiconducting wafers

Read Abstract +

Proceedings Article | 3 February 2007 Paper

Miniature infrared gas sensors using photonic crystals

A. Lambrecht, S. Hartwig, S. Schweizer, R. Wehrspohn

Proc. SPIE. 6480, Photonic Crystal Materials and Devices VI

KEYWORDS: Infrared sensors, Gas sensors, Modulation, Sensors, Etching, Silicon, Photonic crystals, Infrared radiation, Carbon monoxide, Absorption

Read Abstract +

Proceedings Article | 12 May 2006 Paper

Dispersive elements for spectrum splitting in solar cell applications

A. Bielawny, P.-T. Miclea, A. v. Rhein, R. Wehrspohn, S. van Riesen, S. Glunz

Proc. SPIE. 6197, Photonics for Solar Energy Systems

KEYWORDS: Photovoltaics, Diffraction, Optical filters, Solar cells, Lamps, Photonic crystals, Gallium antimonide, Halogens, Indium gallium phosphide, Diffraction gratings

Read Abstract +

Proceedings Article | 1 October 2005 Paper

Nonlinear femtosecond pulse tuning of 2-D photonic crystals

Henry van Driel, H. Tan, S. Schweizer, R. Wehrspohn

Proc. SPIE. 5971, Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics

KEYWORDS: Refractive index, Femtosecond phenomena, Crystals, Dielectrics, Silicon, Reflectivity, Photonic crystals, Kerr effect, Picosecond phenomena, Laser beam diagnostics

Read Abstract +

Proceedings Article | 13 September 2005 Paper

Nonlinear optical tuning in a 2-D silicon photonic crystal

Stefan Schweizer, Ralf Wehrspohn, Hong-Wee Tan, Henry van Driel

Proc. SPIE. 5926, Tuning the Optical Response of Photonic Bandgap Structures II

KEYWORDS: Refractive index, Crystals, Silicon, Reflectivity, Photonic crystals, Kerr effect, Picosecond phenomena, Silicon photonics, Laser beam diagnostics, Absorption

Read Abstract +

Proceedings Article | 13 September 2005 Paper

Director fields of nematic liquid crystals in tunable photonic crystals

Heinz-Siegfried Kitzerow, Guido Mertens, Heinrich Matthias, Heinrich Marsmann, Ralf Wehrspohn, Sven Matthias, Ulrich Goesele, Stefan Frey, Helmut Foell

Proc. SPIE. 5926, Tuning the Optical Response of Photonic Bandgap Structures II

KEYWORDS: Refractive index, Modulation, Silicon, Photonic crystals, Liquid crystal on silicon, Solids, Liquid crystals, Infrared radiation, Semiconducting wafers, Optical microcavities

Read Abstract +

Proceedings Article | 26 August 2005 Paper

Surface enhanced Raman spectroscopy on monodisperse silver and nickel nanowires

P.-T. Miclea, G. Sauer, G. Brehm, S. Schneider, H. Graener, G. Seifert, K. Nielsch, J. Choi, P. Goring, U. Gosele, S. Schweizer, R. Wehrspohn

Proc. SPIE. 5927, Plasmonics: Metallic Nanostructures and Their Optical Properties III

KEYWORDS: Metals, Particles, Molecules, Nickel, Dielectrics, Silver, Surface enhanced Raman spectroscopy, Raman spectroscopy, Mie scattering, Nanowires

Read Abstract +

Proceedings Article | 23 May 2005 Paper

Photonic crystal gas sensors

R. Wehrspohn, T. Geppert, S. Schweizer, A. Rhein, D. Pergande, T. Beyer, Armin Lambrecht

Proc. SPIE. 5855, 17th International Conference on Optical Fibre Sensors

KEYWORDS: Semiconductors, Refractive index, Gas sensors, Sensors, Spectroscopy, Dielectrics, Silicon, Gases, Photonic crystals, Absorption

Read Abstract +

Proceedings Article | 25 October 2004 Paper

High-contrast planar photonic crystals

Reinhard Marz, Sven Burger, Alfred Forchel, Helmut Heidrich, Ortwin Hess, Dirk Michaelis, Klaus Wandel, Ralph Wehrspohn

Proc. SPIE. 5597, Nanophotonics for Communication: Materials and Devices

KEYWORDS: Waveguides, Dispersion, Etching, Photonic crystals, Fiber lasers, Optical networks, Nanophotonics, Optimization (mathematics), Systems modeling, Instrument modeling

Read Abstract +

Proceedings Article | 14 October 2004 Paper

Photonic crystal gas sensors

Torsten Geppert, Stefan Schweizer, J. Schilling, Cecile Jamois, A. V. Rhein, D. Pergande, Regine Glatthaar, P. Hahn, A. Feisst, Armin Lambrecht, Ralf Wehrspohn

Proc. SPIE. 5511, Tuning the Optical Response of Photonic Bandgap Structures

KEYWORDS: Refractive index, Gas sensors, Sensors, Chemical species, Dielectrics, Silicon, Gases, Photonic crystals, Distortion, Absorption

Read Abstract +

Proceedings Article | 14 October 2004 Paper

Tuning 2D photonic crystals

Henry van Driel, Stephen Leonard, Hong-Wee Tan, A. Birner, J. Schilling, Stefan Schweizer, Ralf Wehrspohn, Ulrich Gosele

Proc. SPIE. 5511, Tuning the Optical Response of Photonic Bandgap Structures

KEYWORDS: Refractive index, Optical properties, Crystals, Dielectrics, Silicon, Reflectivity, Photonic crystals, Kerr effect, Liquid crystals, Silicon photonics

Read Abstract +

Proceedings Article | 25 March 2004 Paper

Periodically arranged point defects in a 2D photonic crystal: the photonic analogue to a doped semiconductor

Stefan Richter, Stefan Schweizer, Reinald Hillebrand, Cecile Jamois, Ralf Wehrspohn, Margit Zacharias, Ulrich Goesele

Proc. SPIE. 5277, Photonics: Design, Technology, and Packaging

KEYWORDS: Semiconductors, Diffraction, Resonators, Reflection, Crystals, Dielectrics, Silicon, Reflectivity, Photonic crystals, Scanning electron microscopy

Read Abstract +

Showing 5 of 33 publications

Proceedings Volume Editor (5)

SPIE Conference Volume | 27 August 2018

Photonics for Solar Energy Systems VII

SPIE Conference Volume | 24 June 2016

Photonics for Solar Energy Systems VI

SPIE Conference Volume | 19 May 2014

Photonics for Solar Energy Systems V

SPIE Conference Volume | 15 May 2012

Photonics for Solar Energy Systems IV

SPIE Conference Volume | 10 May 2010

Photonics for Solar Energy Systems III

Conference Committee Involvement (18)