Fraunhofer-Gesellschaft

Publica

Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten.
2021Atmospheric Pressure Dry Etching of Polysilicon Layers for highly Reverse Bias-stable TOPCon Solar Cells
Kafle, B.; Mack, S.; Teßmann, C.; Bashardoust, S.; Clochard, L.; Duffy, E.; Wolf, A.; Hofmann, M.; Rentsch, J.
Zeitschriftenaufsatz
2021Efficiency Potential Analysis of p- and n-Type Epitaxially Grown Si Wafers
Rittmann, C.; Dalke, J.; Drießen, M.; Weiss, C.; Schindler, F.; Sorgenfrei, R.; Schubert, M.C.; Janz, S.
Konferenzbeitrag
2021The Empirical Digital Twin: Representation Learning on Solar Cell Images and Efficient Defect Detection with Human-in-the-Loop
Kunze, P.; Rein, S.; Mueller, T.; Hemsendorf, M.; Ramspeck, K.; Demant, M.
Konferenzbeitrag
2021Extraordinarily High Minority Charge Carrier Lifetime Observed in Crystalline Silicon
Steinhauser, B.; Niewelt, T.; Richter, A.; Eberle, R.; Schubert, M.
Zeitschriftenaufsatz
2021Fast and Accurate Short-Circuit Current versus Irradiance Determination of a Spectrally Nonlinear Solar Cell Using a Spectral Shaping Setup
Mühleis, M.; Kröger, I.; Hohl-Ebinger, J.
Zeitschriftenaufsatz
2021Gallium-Doped Silicon for High-Efficiency Commercial Passivated Emitter and Rear Solar Cells
Grant, N.E.; Altermatt, P.P.; Niewelt, T.; Post, R.; Kwapil, W.; Schubert, M.C.; Murphy, J.D.
Zeitschriftenaufsatz
2021Learning an Empirical Digital Twin from Measurement Images for a Comprehensive Quality Inspection of Solar Cells
Kunze, P.; Rein, S.; Hemsendorf, M.; Ramspeck, K.; Demant, M.
Zeitschriftenaufsatz
2021Parameterization of the Back-Surface Reflection for PERC Solar Cells Including Variation of Back-Contact Coverage
Alapont Sabater, A.; Fell, A.; Brand, A.A.; Müller, M.; Greulich, J.M.
Zeitschriftenaufsatz
2021Programmable Spectral Shaping Demonstrated at the Solar Spectral Irradiance Distribution
Mühleis, M.; Hohl-Ebinger, J.
Zeitschriftenaufsatz
2020Assessment of Influencing Factors on Lifetime-Based Defect Analysis
Post, R.; Niewelt, T.; Kwapil, W.; Schubert, M.C.
Konferenzbeitrag
2020Comparing Microwave Detected Photoconductance, Quasi Steady State Photoconductance and Photoluminiscence Imaging for Iron Analysis in Silicon
Pengerla, M.; Al-Hajjawi, S.; Kuruganti, V.; Haunschild, J.; Schüler, N.; Dornich, K.; Rein, S.
Konferenzbeitrag
2020The Crystal Growth Explorer: Real-Time Navigable 3D Visualization of Silicon Grains and Defect Related Data in Cast-Mono and Multicrystalline Bricks
Schönauer, J.; Demant, M.; Trötschler, T.; Kovvali, A.S.; Schremmer, H.; Krenckel, P.; Riepe, S.; Rein, S.
Konferenzbeitrag
2020Efficient Deployment of Deep Neural Networks for Quality Inspection of Solar Cells using Smart Labeling
Kunze, P.; Greulich, J.; Rein, S.; Ramspeck, K.; Hemsendorf, M.; Vetter, A.; Demant, M.
Konferenzbeitrag
2020Evaluation of Inline High-Intensity Illumination Treatments against LeTID
Vahlman, H.; Roder, S.; Krauß, K.; Nekarda, J.; Rein, S.
Konferenzbeitrag
2020LeTID- and (Extended) BO-Related Degradation and Regeneration in B- and Ga-Doped Monocrystalline Silicon during Dark and Illuminated Anneals
Kwapil, W.; Dalke, J.; Niewelt, T.; Schubert, M.C.
Konferenzbeitrag
2020Machine Learning for Advanced Solar Cell Production. Adversarial Denoising, Sub-pixel Alignment and the Digital Twin
Demant, M.; Kurumundayil, L.; Kunze, P.; Woernhoer, A.; Kovvali, A.; Rein, S.
Vortrag
2020Measurement Uncertainties in I-V Calibration of Multi-Junction Solar Cells for Different Solar Simulators and Reference Devices
Reichmuth, S.K.; Siefer, G.; Schachtner, M.; Mühleis, M.; Hohl-Ebinger, J.; Glunz, S.W.
Zeitschriftenaufsatz
2020Review and Recent Development in Combining Photoluminescence- and Electroluminescence-Imaging with Carrier Lifetime Measurements via Modulated Photoluminescence at Variable Temperatures
Höffler, H.; Schindler, F.; Brand, A.; Herrmann, D.; Eberle, R.; Post, R.; Kessel, A.; Greulich, J.; Schubert, M.C.
Konferenzbeitrag
2019Accurate Measurement of Bifacial Solar Cells with Single- and Both-Sided Illumination
Rauer, Michael; Guo, Fan; Hohl-Ebinger, Jochen
Konferenzbeitrag
2019Analysis of Temperature Dependent Characteristics of Diffused Regions in Silicon Solar Cells
Eberle, R.; Fell, A.; Richter, A.; Niewelt, T.; Schindler, F.; Schubert, M.
Konferenzbeitrag
2019Contactless determination of base resistivity on silicon wafers with highly doped surfaces
Höffler, H.; Brand, A.A.; Wirtz, W.; Greulich, J.
Zeitschriftenaufsatz
2019Contactless transient carrier spectroscopy and imaging technique using lock-in free carrier emission and absorption
Rougieux, Fiacre E.; Kwapil, Wolfram; Heinz, Friedemann D.; Siriwardhana, Manjula; Schubert, Martin C.
Zeitschriftenaufsatz
2019Correlation of defect luminescence and recombination in multicrystalline silicon
Wyller, Guro Marie; Schindler, Florian; Kwapil, Wolfram; Schön, Jonas; Olsen, Espen; Haug, Halvard; Riepe, Stephan; Schubert, Martin C.
Zeitschriftenaufsatz
2019Edge Recombination Analysis of Silicon Solar Cells Using Photoluminescence Measurements
Stolzenburg, H.; Fell, A.; Schindler, F.; Kwapil, W.; Richter, A.; Baliozan, P.; Schubert, M.C.
Konferenzbeitrag
2019Extracting Metal and Edge Recombination Parameters which are Compatible with Multi-Dimensional Cell Simulations
Saint-Cast, P.; Herrmann, D.; Baliozan, P.; Stolzenburg, H.; Höffler, H.; Fell, A.
Konferenzbeitrag
2019Front Side Structures in TiO2 for Crystalline Silicon Solar Cells. Which Effects can they Achieve?
Stevens, L.; Hauser, H.; Höhn, O.; Tucher, N.; Wellens, C.; Stauch, C.; Jahn, R.; Müller, C.; Bläsi, B.
Konferenzbeitrag
2019Hydrosilane-Free Low-Cost APCVD of SiO2 Films for Crystalline Si Solar Cell Applications
Nagel, H.; Issa, E.; Nagel, T.; Glatthaar, M.; Glunz, S.W.
Konferenzbeitrag
2019Influence of Fundamental Model Uncertainties on Silicon Solar Cell Efficiency Simulations
Wasmer, S.; Fell, A.; Greulich, J.M.
Zeitschriftenaufsatz
2019Investigation of LeTID where we can Control it - Application of FZ Silicon for Defect Studies
Niewelt, T.; Post, R.; Schindler, F.; Kwapil, W.; Schubert, M.C.
Konferenzbeitrag
2019Learning Quality Rating of As-Cut mc-Si Wafers via Convolutional Regression Networks
Demant, M.; Virtue, P.; Kovvali, A.; Yu, S.X.; Rein, S.
Zeitschriftenaufsatz
2019Loss Analysis in Perovskite Photovoltaic Modules
Rakocevic, Lucija; Mundt, Laura; Gehlhaar, Robert; Merckx, Tamara; Aernouts, Tom; Schubert, Martin C.; Glunz, Stefan W.; Poortmans, Jef
Zeitschriftenaufsatz
2019Measurement Uncertainties in the Calibration of Multi-Junction Solar Cells using Different Sun Simulators and Reference Devices
Reichmuth, S.K.; Siefer, Gerald; Schachtner, Michael; Mühleis, Matthias; Hohl-Ebinger, Jochen; Glunz, Stefan W.
Konferenzbeitrag
2019A Novel TLM Analysis for Solar Cells
Mir, H.; Arya, V.; Höffler, H.; Brand, A.
Zeitschriftenaufsatz
2019Re-evaluation of the SRH-Parameters for the FeGa Defect
Post, R.; Niewelt, T.; Yang, W.; Macdonald, D.; Kwapil, W.; Schubert, M.C.
Konferenzbeitrag
2019Visualizing Material Quality and Similarity of mc-Si Wafers Learned by Convolutional Regression Networks
Demant, M.; Virtue, P.; Kovvali, A.; Yu, S.X.; Rein, S.
Zeitschriftenaufsatz
2018Approach for a Holistic Optimization from Wafer to PV System
Mittag, M.; Reise, C.; Wöhrle, N.; Eberle, R.; Schubert, M.; Heinrich, M.
Konferenzbeitrag
2018Challenges for the Quantification of Metal Induced Recombination Losses
Herrmann, D.; Lohmüller, S.; Höffler, H.; Fell, A.; Brand, A.A.; Wolf, A.
Konferenzbeitrag
2018Deep Learning Approach to Inline Quality Rating and Mapping of Multi-Crystalline Si-Wafers
Demant, M.; Virtue, P.; Kovvali, A.S.; Yu, S.X.; Rein, S.
Konferenzbeitrag
2018Inline Characterization of Diamond Wire Sawn Multicrystalline Silicon Wafers
Haunschild, J.; Bergmann, N.; Hammer, T.; Krieg, K.; Kaden, T.; Anspach, O.; Schremmer, H.; Rein, S.
Konferenzbeitrag
2018Inline Wafer Identification Using Optical Character Recognition (OCR)
Al-Hajjawi, S.; Hammer, T.; Haunschild, J.
Konferenzbeitrag
2018An open source based repository for defects in silicon
Juhl, Mattias K.; Heinz, Friedemann D.; Coletti, Gianluca; Macdonald, Daniel; Rougieux, Fiacre E.; Schindler, Florian; Niewelt, Tim; Schubert, Martin C.
Konferenzbeitrag
2018Prediction of Local Temperature Dependent Performance of Silicon Solar Cells
Eberle, R.; Fell, A.; Mägdefessel, S.; Schindler, F.; Schubert, M.C.
Konferenzbeitrag
2018The principle of adaptive excitation for photoluminescence imaging of silicon: Theory
Heinz, Friedemann D.; Zhu, Yan; Hameri, Ziv; Juhl, Mattias; Trupke, Thorsten; Schubert, Martin C.
Zeitschriftenaufsatz
2018Taking monocrystalline silicon to the ultimate lifetime limit
Niewelt, Tim; Richter, Armin; Kho, T.C.; Grant, N.E.; Bonilla, R.S.; Steinhauser, Bernd; Polzin, Jana-Isabelle; Feldmann, Frank; Hermle, Martin; Murphy, J.D.; Phang, S.P.; Kwapil, Wolfram; Schubert, Martin C.
Zeitschriftenaufsatz
2017Angle-dependent reflectance of isotextured silicon
Alapont Sabater, A.; Greulich, J.; Tucher, N.; Bläsi, B.; Glunz, S.W.
Konferenzbeitrag
2017Approaching 22% efficiency with multicrystalline n-type silicon solar cells
Benick, J.; Müller, R.; Schindler, F.; Richter, A.; Hauser, H.; Feldmann, F.; Krenckel, P.; Riepe, S.; Schubert, M.C.; Hermle, M.; Glunz, S.W.
Konferenzbeitrag
2017High performance multicrystalline silicon: Grain structure and iron precipitation
Autruffe, Antoine; M'hamdi, Mohammed; Schindler, Florian; Heinz, Friedemann D.; Ekstrøm, Kai Erik; Schubert, Martin C.; Sabatino, Marisa di; Stokkan, Gaute
Zeitschriftenaufsatz
2017Identification of defect-suppressing grain boundaries in multicrystalline silicon based on measurements of as-cut wafers using advanced image processing
Strauch, T.; Demant, M.; Krenckel, P.; Riepe, S.; Rein, S.
Konferenzbeitrag
2017Light-induced activation and deactivation of bulk defects in boron-doped float-zone silicon
Niewelt, T.; Selinger, M.; Grant, N.; Kwapil, W.M.; Murphy, J.D.; Schubert, M.C.
Zeitschriftenaufsatz
2017Superacid-treated silicon surfaces: Extending the limit of carrier lifetime for photovoltaic applications
Grant, N.E.; Niewelt, T.; Wilson, N.R.; Wheeler-Jones, E.C.; Bullock, J.; Al-Amin, M.; Schubert, M.C.; Veen, A.C. van; Javey, A.; Murphy, J.D.
Zeitschriftenaufsatz
2016Alternative Inline Analysis of Acidic Etching Baths
Mohr, L.; Dannenberg, T.; Zimmer, M.; Rentsch, J.
Konferenzbeitrag
2016Analysis of grain structure evolution via image processing based on optical measurements of mc Si wafers
Strauch, T.; Demant, M.; Krenckel, P.; Riepe, S.; Rein, S.
Konferenzbeitrag
2016Material limits of silicon from state-of-the-art photoluminescence imaging techniques
Schindler, F.; Giesecke, J.; Michl, B.; Schön, J.; Krenckel, P.; Riepe, S.; Warta, W.; Schubert, M.C.
Konferenzbeitrag
2016Microcracks in silicon wafers I: Inline detection and implications of crack morphology on wafer strength
Demant, M.; Welschehold, T.; Oswald, M.; Bartsch, S.; Brox, T.; Schoenfelder, S.; Rein, S.
Zeitschriftenaufsatz
2016Microcracks in silicon wafers II: Implications on solar cell characteristics, statistics and physical origin
Demant, M.; Welschehold, T.; Kluska, S.; Rein, S.
Zeitschriftenaufsatz
2016PC1Dmod 6.2 - improved simulation of c-Si devices with updates on device physics and user interface
Haug, H.; Greulich, J.
Zeitschriftenaufsatz
2015Carrier recombination at metallic precipitates in p- and n-type silicon
Kwapil, W.; Schön, J.; Warta, W.; Schubert, M.C.
Zeitschriftenaufsatz
2015Passivation-induced cavity defects in laser-doped selective emitter Si solar cells - formation model and recombination analysis
Geisler, C.; Kluska, S.; Hopman, S.; Glatthaar, M.
Zeitschriftenaufsatz
2015Potential gain in multicrystalline silicon solar cell efficiency by n-Type doping
Schindler, F.; Michl, B.; Kleiber, A.; Steinkemper, H.; Schön, J.; Kwapil, W.; Krenckel, P.; Riepe, S.; Warta, W.; Schubert, M.C.
Zeitschriftenaufsatz
2014The BOSCO solar cell: Simulation and experiment
Fertig, F.; Greulich, J.; Krauss, K.; Clement, F.; Biro, D.; Preu, R.; Rein, S.
Zeitschriftenaufsatz
2014Fast hot spot evaluation
Geisemeyer, I.; Fertig, F.; Warta, W.; Rein, S.; Schubert, M.
Konferenzbeitrag
2014Inline processes for the stabilization of p-type crystalline Si solar cells against potential-induced degradation
Nagel, N.; Saint-Cast, P.; Glatthaar, M.; Glunz, S.W.
Konferenzbeitrag
2014Micro-cracks in silicon wafers and solar cells: Detection and rating of mechanical strength and electrical quality
Demant, M.; Oswald, M.; Welschehold, T.; Nold, S.; Bartsch, S.; Schoenfelder, S.; Rein, S.
Konferenzbeitrag
2014The potential of multicrystalline n-type silicon for high efficiency solar cells
Schindler, F.; Michl, B.; Kleiber, A.; Steinkemper, H.; Schön, J.; Kwapil, W.; Krenckel, P.; Riepe, S.; Warta, W.; Schubert, M.C.
Konferenzbeitrag
2014Solar cell efficiency losses due to impurities from the crucible in multicrystalline silicon
Schindler, F.; Michl, B.; Schön, J.; Kwapil, W.; Warta, W.; Schubert, M.
Zeitschriftenaufsatz
2013Evaluation and improvement of a feature-based classification framework to rate the quality of multicrystalline silicon wafers
Demant, M.; Höffler, H.; Schwaderer, D.; Seidl, A.; Haunschild, J.; Rein, S.
Konferenzbeitrag
2013Flexographic printing - high throughput technology for fine line seed layer printing on silicon solar cells
Lorenz, A.; Kalio, A.; Hofmeister, G.; Nold, S.; Kraft, A.; Bartsch, J.; Wolf, D.; Dreher, M.; Clement, F.; Biro, D.
Konferenzbeitrag
2013The impact of different diffusion temperature profiles on iron concentrations and carrier lifetimes in multicrystalline silicon wafers
Michl, B.; Schön, J.; Warta, W.; Schubert, M.C.
Zeitschriftenaufsatz
2013Industrial screen-printed solar cells with novel atmospheric pressure dry texturing process
Kafle, B.; Trogus, D.; Dresler, B.; Mäder, G.; Clochard, L.; Duffy, E.; Hofmann, M.; Rentsch, J.
Konferenzbeitrag
2013Influence of argon flow rate on melt convection and incorporation of SiC in multicrystalline silicon
Schmid, C.; Schumann, M.; Haas, F.; Riepe, S.
Konferenzbeitrag
2013Material limitations due to crucible impurities in multicrystalline silicon for high efficiency solar cells
Schindler, F.; Michl, B.; Schön, J.; Kwapil, W.; Warta, W.; Schubert, M.C.
Konferenzbeitrag
2013Passivation of solar cell emitters using aluminum nitride
Krugel, G.; Sharma, A.; Moldovan, A.; Wolke, W.; Rentsch, J.; Preu, R.
Konferenzbeitrag
2013Stability of the regeneration of the boron-oxygen complex in silicon solar cells during module integration
Fertig, F.; Greulich, J.; Broisch, J.; Biro, D.; Rein, S.
Zeitschriftenaufsatz
2012Tomographic defect reconstruction of multicrystalline silicon ingots using photoluminescence images of As-Cut wafers and solar cells
Zeidler, R.; Haunschild, J.; Seeber, B.; Riepe, S.; Höffler, H.; Fertig, F.; Reis, I.; Rein, S.
Konferenzbeitrag
2011Can luminescence imaging replace lock-in thermography on solar cells?
Breitenstein, O.; Warta, W.; Schubert, M.C.; Kwapil, W.; Müller, J.; Hinken, D.; Bothe, K.; Bauer, J.
Zeitschriftenaufsatz
2011Comprehensive characterization of advanced cell concepts with sub-micron resolution
Gundel, P.; Drießen, M.; Bartsch, J.; Jäger, U.; Suwito, D.; Heinz, F.D.; Warta, W.; Schubert, M.C.
Konferenzbeitrag
2011Comprehensive microscopic analysis of laser-induced high doping regions in silicon
Gundel, P.; Suwito, D.; Jäger, U.; Heinz, F.D.; Warta, W.; Schubert, M.C.
Zeitschriftenaufsatz
2011From Injection Dependent Lifetime to Solar Cell Efficiency
Michl, B.; Rüdiger, M.; Giesecke, J.A.; Hermle, M.; Warta, W.; Schubert, M.C.
Konferenzbeitrag
2011Imaging of metastable defects in silicon
Schubert, M.C.; Habenicht, H.; Warta, W.
Zeitschriftenaufsatz
2011Impact of Impurities on the Mechanical Strength of Multicrystalline Silicon
Orellana Perez, T.; Funke, C.; Fütterer, W.; Riepe, S.; Möller, H.J.; Tejado Garrido, E.M.; Pastor Caño, J.Y.
Konferenzbeitrag
2011Understanding junction breakdown in multicrystalline solar cells
Breitenstein, O.; Bauer, J.; Bothe, K.; Kwapil, W.; Lausch, D.; Rau, U.; Schmidt, J.; Schneemann, M.; Schubert, M.C.; Wagner, J.-M.; Warta, W.
Zeitschriftenaufsatz
2011Understanding the distribution of iron in multicrystalline silicon after emitter formation
Schön, J.; Habenicht, H.; Schubert, M.C.; Warta, W.
Zeitschriftenaufsatz
20102D modeling of the iron concentration from crystallization to final firing of mc silicon solar cells
Schön, J.; Schubert, M.C.; Habenicht, H.; Warta, W.
Konferenzbeitrag
2010Accurate IV-measurement for back contact solar cells
Glatthaar, M.; Hohl-Ebinger, J.; Krieg, A.; Greif, M.; Greco, L.; Clement, F.; Rein, S.; Warta, W.; Preu, R.
Konferenzbeitrag
2010Analysis of luminescence images applying pattern recognition techniques
Demant, M.; Glatthaar, M.; Haunschild, J.; Rein, S.
Konferenzbeitrag
2010Approach to the physical origin of breakdown in silicon solar cells by optical spectroscopy
Gundel, P.; Kwapil, W.; Schubert, M.C.; Seifert, H.; Warta, W.
Zeitschriftenaufsatz
2010Cause of increased currents under reverse-bias conditions of upgraded metallurgical grade multicrystalline silicon solar cells
Kwapil, W.; Wagner, M.; Schubert, M.C.; Warta, W.
Konferenzbeitrag
2010Characterisation of local Al-BSF formation for PERC solar cell structures
Grasso, F.S.; Gautero, L.; Rentsch, J.; Preu, R.; Lanzafame, R.
Konferenzbeitrag
2010Characterization and optimization of laser edge isolation
Gutscher, S.; Knorz, A.; Gundel, P.; Greulich, J.; Preu, R.
Konferenzbeitrag
2010Conductivity mobility and hall mobility in compensated multicrystalline silicon
Schindler, F.; Geilker, J.; Kwapil, W.; Giesecke, J.; Schubert, M.C.; Warta, W.
Konferenzbeitrag
2010Determining the minority carrier lifetime in crystalline silicon thin-film material
Rosenits, P.; Kopp, F.; Walter, D.; Reber, S.; Warta, W.
Konferenzbeitrag
2010Determining the minority carrier lifetime in epitaxial silicon layers by micro-wave-detected photoconductivity measurements
Walter, D.; Rosenits, P.; Kopp, F.; Reber, S.; Berger, B.; Warta, W.
Konferenzbeitrag
2010Doping concentration and mobility in compensated material: Comparison of different determination methods
Geilker, J.; Kwapil, W.; Reis, I.; Rein, S.
Konferenzbeitrag
2010Doping- and carrier concentration profile characterisation of highly phosphorus-doped emitters
Werner, S.; Belledin, U.; Kimmerle, A.; Fallisch, A.; Wolf, A.; Biro, D.
Konferenzbeitrag
2010Impact of stress on recombination of metal precipitates in silicon
Gundel, P.; Schubert, M.C.; Heinz, F.D.; Kwapil, W.; Warta, W.; Martinez-Criado, G.; Reiche, M.; Weber, E.R.
Zeitschriftenaufsatz
2010Luminescence imaging for quantitative solar cell material and process characterization
Glatthaar, M.; Haunschild, J.; Zeidler, R.; Rentsch, J.; Rein, S.; Breitenstein, O.; Hinken, D.; Bothe, K.
Konferenzbeitrag
2010Mapping the quantitative carrier lifetime and doping concentration with micro resolution
Heinz, F.D.; Gundel, P.; Schubert, M.C.; Warta, W.
Konferenzbeitrag
2010Photoluminescence imaging of chromium in crystalline silicon
Habenicht, H.; Schubert, M.C.; Coletti, G.; Warta, W.
Konferenzbeitrag
2010Recombination activity enhancement by stress in silicon
Gundel, P.; Schubert, M.C.; Heinz, F.D.; Warta, W.
Konferenzbeitrag
2010The role of material quality in EWT and standard solar cells on multicrystalline standard and UMG silicon material
Schubert, M.C.; Rüdiger, M.; Michl, B.; Schindler, F.; Kwapil, W.; Giesecke, J.; Hermle, M.; Warta, W.; Ferré, R.; Wade, R.; Petter, K.
Konferenzbeitrag
2010Simultaneous determination of carrier lifetime and net dopant concentration of silicon wafers from photoluminescence
Giesecke, J.A.; Walter, D.; Kopp, F.; Rosenits, P.; Schubert, M.C.; Warta, W.
Konferenzbeitrag