Prof. Ralf B. Wehrspohn Profile

Prof. Ralf B. Wehrspohn

at Martin Luther Univ Halle Wittenberg

SPIE Involvement:

Author | Editor

Publications (36)

Proceedings Article | 19 June 2024 Presentation

Anti-Reflective Graded-Index Metasurface with Correlated Disorder for Light Management in Planar Solar Cells

Prerak Dhawan, Carsten Rockstuhl, Maria Gaudig, Peter Piechulla, Alexander Sprafke, Ralf Wehrspohn

Proceedings Volume PC13014, PC1301408 (2024) https://doi.org/10.1117/12.3024869

KEYWORDS: Solar cells, Diseases and disorders, Antireflective coatings, Nanostructures, Dielectrics, Design, Wafer level optics, Semiconducting wafers, Scattering, Photocurrent

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Proceedings Article | 30 May 2022 Presentation

Nearly hyperuniform antireflection coatings made from high-index nanodisks for silicon heterojunction solar cells

Peter Piechulla, Evgeniia Slivina, Derk Baetzner, Ivan Fernandez-Corbaton, Prerak Dhawan, Ralf Wehrspohn, Alexander Sprafke, Carsten Rockstuhl

Proceedings Volume PC12150, PC121500E (2022) https://doi.org/10.1117/12.2624092

KEYWORDS: Solar cells, Heterojunctions, Silicon, Antireflective coatings, Scattering, Reflectivity, Particles, Coating, Active optics, Titanium dioxide

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Proceedings Article | 5 March 2021 Presentation

Light-trapping structures for planar solar cells based on Schwarz-Christoffel mappings

Prerak Dhawan, Carsten Rockstuhl, Ralf Wehrspohn, Alexander Sprafke, Maria Gaudig

Proceedings Volume 11681, 1168107 (2021) https://doi.org/10.1117/12.2582567

KEYWORDS: Solar cells, Volume rendering, Thin films, Absorption, Thin film deposition, Stochastic processes, Refractive index, Optical lithography, Nanostructuring, Nanostructures

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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

Proceedings Volume 10688, 106880R (2018) https://doi.org/10.1117/12.2315800

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

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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

Proceedings Volume 9898, 989816 (2016) https://doi.org/10.1117/12.2239183

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

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Proceedings Article | 16 September 2013 Paper

Nanowires from dirty multi-crystalline Si for hydrogen generation

Xiaopeng Li, Stefan Schweizer, Alexander Sprafke, Ralf Wehrspohn

Proceedings Volume 8822, 88220U (2013) https://doi.org/10.1117/12.2024231

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

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Proceedings Article | 11 September 2013 Paper

3D photonic crystals for photon management in solar cells

S. Schweizer, A. Sprafke, R. Wehrspohn

Proceedings Volume 8808, 880804 (2013) https://doi.org/10.1117/12.2026250

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

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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

Proceedings Volume 8438, 84380M (2012) https://doi.org/10.1117/12.923748

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

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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

Proceedings Volume 8438, 843817 (2012) https://doi.org/10.1117/12.922380

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

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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

Proceedings Volume 8095, 809508 (2011) https://doi.org/10.1117/12.904994

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

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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

Proceedings Volume 7756, 77560A (2010) https://doi.org/10.1117/12.859467

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

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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

Proceedings Volume 7725, 77250K (2010) https://doi.org/10.1117/12.857614

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

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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

Proceedings Volume 7725, 772513 (2010) https://doi.org/10.1117/12.853717

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

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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

Proceedings Volume 7725, 772505 (2010) https://doi.org/10.1117/12.854596

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

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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

Proceedings Volume 7725, 772519 (2010) https://doi.org/10.1117/12.854573

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

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Proceedings Article | 18 May 2010 Paper

Strain dependence of second-harmonic generation in silicon

Clemens Schriever, Christian Bohley, Jörg Schilling, Ralf Wehrspohn

Proceedings Volume 7719, 77190Z (2010) https://doi.org/10.1117/12.854520

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

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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

Proceedings Volume 7393, 73930S (2009) https://doi.org/10.1117/12.824862

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

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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

Proceedings Volume 7409, 74090J (2009) https://doi.org/10.1117/12.824688

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

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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

Proceedings Volume 7362, 73620S (2009) https://doi.org/10.1117/12.821645

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

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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

Proceedings Volume 7002, 70020A (2008) https://doi.org/10.1117/12.781248

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

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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

Proceedings Volume 7002, 700208 (2008) https://doi.org/10.1117/12.781090

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

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Proceedings Article | 5 May 2008 Paper

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

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

Proceedings Volume 7002, 70020W (2008) https://doi.org/10.1117/12.781111

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

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Proceedings Article | 21 April 2008 Paper

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

Benjamin Gesemann, Stefan Schweizer, Ralf Wehrspohn

Proceedings Volume 6989, 69890T (2008) https://doi.org/10.1117/12.781028

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

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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

Proceedings Volume 6651, 665106 (2007) https://doi.org/10.1117/12.733084

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

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Proceedings Article | 7 March 2007 Paper

Silicon-based low-loss photonic crystal waveguides

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

Proceedings Volume 6475, 647511 (2007) https://doi.org/10.1117/12.699892

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

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Proceedings Article | 3 February 2007 Paper

Miniature infrared gas sensors using photonic crystals

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

Proceedings Volume 6480, 64800D (2007) https://doi.org/10.1117/12.700792

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

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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

Proceedings Volume 6197, 619704 (2006) https://doi.org/10.1117/12.662567

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

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Proceedings Article | 1 October 2005 Paper

Nonlinear femtosecond pulse tuning of 2-D photonic crystals

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

Proceedings Volume 5971, 59710J (2005) https://doi.org/10.1117/12.628670

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

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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

Proceedings Volume 5926, 59260C (2005) https://doi.org/10.1117/12.616985

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

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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

Proceedings Volume 5926, 592605 (2005) https://doi.org/10.1117/12.616456

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

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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

Proceedings Volume 5927, 59270O (2005) https://doi.org/10.1117/12.616315

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

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Proceedings Article | 23 May 2005 Paper

Photonic crystal gas sensors

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

Proceedings Volume 5855, (2005) https://doi.org/10.1117/12.623381

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

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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

Proceedings Volume 5597, (2004) https://doi.org/10.1117/12.580070

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

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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

Proceedings Volume 5511, (2004) https://doi.org/10.1117/12.559914

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

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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

Proceedings Volume 5511, (2004) https://doi.org/10.1117/12.561724

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

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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

Proceedings Volume 5277, (2004) https://doi.org/10.1117/12.522063

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

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Showing 5 of 36 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)