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Dive into the research topics where Karsten von Maydell is active.

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Featured researches published by Karsten von Maydell.


Journal of Applied Physics | 2011

Three dimensional optical modeling of amorphous silicon thin film solar cells using the finite-difference time-domain method including real randomly surface topographies

J. Lacombe; Oleg Sergeev; Kambulakwao Chakanga; Karsten von Maydell; Carsten Agert

In this paper, modeling of light propagation in silicon thin film solar cells without using any fitting parameter is presented. The aim is to create a realistic view of the light trapping effects and of the resulting optical generation rate in the absorbing semiconductor layers. The focus is on real three dimensional systems. Our software Sentaurus tcad, developed by Synopsys, has the ability to import real topography measurements and to model the light propagation using the finite-difference time-domain method. To verify the simulation, we compared the measured and simulated angular distribution functions of a glass/SnO2:F transparent conducting oxide system for different wavelengths. The optical generation rate of charge carriers in amorphous silicon thin film solar cells including rough interfaces is calculated. The distribution of the optical generation rate is correlated with the shape of the interface, and the external quantum efficiencies are calculated and compared to experimental data.


ACS Applied Materials & Interfaces | 2015

Semitransparent Polymer-Based Solar Cells with Aluminum-Doped Zinc Oxide Electrodes

Sebastian Wilken; Verena Wilkens; Dorothea Scheunemann; R.-E. Nowak; Karsten von Maydell; Jürgen Parisi; Holger Borchert

With the use of two transparent electrodes, organic polymer-fullerene solar cells are semitransparent and may be combined to parallel-connected multijunction devices or used for innovative applications like power-generating windows. A challenging issue is the optimization of the electrodes, to combine high transparency with adequate electric properties. In the present work, we study the potential of sputter-deposited aluminum-doped zinc oxide as an alternative to the widely used but relatively expensive indium tin oxide (ITO) as cathode material in semitransparent polymer-fullerene solar cells. Concerning the anode, we utilized an insulator-metal-insulator structure based on ultrathin Au films embedded between two evaporated MoO3 layers, with the outer MoO3 film (capping layer) serving as a light coupling layer. The performance of the ITO-free semitransparent polymer-fullerene solar cells was systematically studied as dependent on the thickness of the capping layer and the active layer as well as the illumination direction. These variations were found to have strong impact on the obtained photocurrent densities. We performed optical simulations of the electric field distribution within the devices using the transfer-matrix method, to analyze the origin of the current density variations in detail and provide deep insight into the device physics. With the conventional absorber materials studied here, optimized ITO-free and semitransparent devices reached 2.0% power conversion efficiency and a maximum optical transmission of 60%, with the device concept being potentially transferable to other absorber materials.


Applied Physics Letters | 2014

Enhanced passivation at amorphous/crystalline silicon interface and suppressed Schottky barrier by deposition of microcrystalline silicon emitter layer in silicon heterojunction solar cells

Omid Madani Ghahfarokhi; Karsten von Maydell; Carsten Agert

In silicon heterojunction (SHJ) solar cells, the embedded p-layer (emitter) between transparent conductive oxide (TCO) and crystalline silicon is depleted form both sides. Hence, high level of doping is required to preserve flat band. In this report, the role of the emitter conductivity on the electrical properties of SHJ solar cells is investigated. We offer depositing microcrystalline silicon (μc-Si) films to satisfy the required emitter conductivity and to suppress the Schottky barrier when employing low work function TCO material. Finally, by depositing μc-Si layers, the passivation of solar cell precursors improves and current increases, due to their low absorption coefficient.


Journal of Physical Chemistry Letters | 2014

Comparison of Ag and SiO2 Nanoparticles for Light Trapping Applications in Silicon Thin Film Solar Cells.

Martin Theuring; Peng Hui Wang; Martin Vehse; Volker Steenhoff; Karsten von Maydell; Carsten Agert; Alexandre G. Brolo

Plasmonic and photonic light trapping structures can significantly improve the efficiency of solar cells. This work presents an experimental and computational comparison of identically shaped metallic (Ag) and nonmetallic (SiO2) nanoparticles integrated to the back contact of amorphous silicon solar cells. Our results show comparable performance for both samples, suggesting that minor influence arises from the nanoparticle material. Particularly, no additional beneficial effect of the plasmonic features due to metallic nanoparticles could be observed.


Optics Express | 2015

Laser perforated ultrathin metal films for transparent electrode applications

Martin Theuring; Volker Steenhoff; S. Geißendörfer; Martin Vehse; Karsten von Maydell; Carsten Agert

Transmittance and conductivity are the key requirements for transparent electrodes. Many optoelectronic applications require additional features such as mechanical flexibility and cost-efficient fabrication at low temperatures. Here we demonstrate a simple method to fabricate high performance transparent electrodes that is based on perforation of thin silver layers using picosecond laser pulses. Transparent electrodes have been characterized optically and electrically in order to determine the influence of specific surface coverage. Special attention was paid to maintaining sufficient conductivity in the metal-free areas. As a result, transmittance of a much higher bandwidth was achieved as compared to unpatterned metal films. Transparent electrodes have been fabricated on glass and plastic foil, as well as wafer-based silicon heterojunction solar cells, demonstrating their applicability for most relevant cases.


IEEE Journal of Photovoltaics | 2015

Optimizing Folded Silicon Thin-Film Solar Cells on ZnO Honeycomb Electrodes

R.-E. Nowak; S. Geißendörfer; Kambulakwao Chakanga; Maren Juilfs; Nies Reininghaus; Martin Vehse; Karsten von Maydell; Carsten Agert

A promising approach for low-cost nanostructured thin-film solar cells with enhanced absorption is the fabrication of zinc oxide (ZnO) honeycomb electrodes in a combined bottom-up process of nanosphere lithography and electrochemical deposition. To optimize the honeycomb structures, we investigate thin hydrogenated amorphous silicon (a-Si:H) solar cells (with 100 nm absorber thickness) on honeycomb electrodes with different periodicities in optical and electrical simulations; whereas the electrical performance is not significantly affected with changing periodicity, the short-circuit current density is reduced for increasing honeycomb diameter due to increased parasitic absorption of the electrochemically deposited ZnO. Furthermore, we demonstrate that for micromorph tandem solar cells with an intrinsic layer thickness of hydrogenated microcrystalline silicon (μc-Si:H) of >500 nm, a focusing effect occurs, which leads to a strong enhancement in the quantum efficiency in the microcrystalline bottom solar cell.


Applied Physics Letters | 2014

Cost-effective nanostructured thin-film solar cell with enhanced absorption

Peng Hui Wang; R.-E. Nowak; S. Geißendörfer; Martin Vehse; Nies Reininghaus; Oleg Sergeev; Karsten von Maydell; Alexandre G. Brolo; Carsten Agert

Nanostructured transparent conductive electrodes are highly interesting for efficient light management in thin-film solar cells, but they are often costly to manufacture and limited to small scales. This work reports on a low-cost and scalable bottom-up approach to fabricate nanostructured thin-film solar cells. A folded solar cell with increased optical absorber volume was deposited on honeycomb patterned zinc oxide nanostructures, fabricated in a combined process of nanosphere lithography and electrochemical deposition. The periodicity of the honeycomb pattern can be easily varied in the fabrication process, which allows structural optimization for different absorber materials. The implementation of this concept in amorphous silicon thin-film solar cells with only 100 nm absorber layer was demonstrated. The nanostructured solar cell showed approximately 10% increase in the short circuit current density compared to a cell on an optimized commercial textured reference electrode. The concept presented here...


Journal of Photonics for Energy | 2014

Laser textured substrates for light in-coupling in thin-film solar cells

Kambulakwao Chakanga; Ortwin Siepmann; Oleg Sergeev; S. Geißendörfer; Karsten von Maydell; Carsten Agert

Abstract. In this work, we investigate the use of a picosecond (ps) laser used for monolithic connection to texture three commercially available and frequently used multicomponent glasses, Corning EAGLE XG®, Schott BOROFLOAT® 33 and Saint-Gobain SGG DIAMANT®. The results show that the ablated crater profile and degree of texturing are glass composition dependent. This might be attributed to the different laser-induced electron collision times and recombination rates, and thus the critical electron density evolution leading to ablation. The surface texture is altered from periodic to random with decreasing scribing speed. The transmission of the textured substrates gradually decreases, whereas the multireflection on the surface increases as a consequence of the topological and morphological changes. The angular resolved measurements illustrate that the textured glass substrates scatter the light toward greater angles, which is necessary to increase the effective optical path in the absorber layer. Simulation results show that textured glass increases the absorption in the absorber material and the slightly modified refractive index region around the crater does not counteract the light in-coupling effect. The results suggest that these substrates can be used in various photovoltaic technologies and show potential for the application of alternative front contacts, such as carbon nanotubes.


Applied Physics Letters | 2013

Correlation between optical emission spectroscopy of hydrogen/germane plasma and the Raman crystallinity factor of germanium layers

P. Klement; C. Feser; B. Hanke; Karsten von Maydell; Carsten Agert

Optical emission measurements were recorded during microcrystalline germanium layer growth on glass with plasma enhanced chemical vapor deposition. A significant difference for the intensities of SiH and GeH could be identified in the optical emission spectra of hydrogen/silane (H2/SiH4) and hydrogen/germane (H2/GeH4) plasma. In H2/SiH4 plasma, Si and SiH are present, whereas Ge but no GeH could be detected in H2/GeH4 plasma. The specific Raman crystallinity factor (ϕc) was evaluated for the layers after deposition. In H2/GeH4 plasma, the ratio of optical emission intensities of Hα (I(Hα), λ = 656.28 nm) and Ge (I(Ge), λ = 303.90 nm) is proportional to ϕc,Ge.


Optical Engineering | 2012

Optical modeling of thin-film silicon solar cells by combination of the transfer-matrix method and the raytracer algorithm

Cordula Walder; Juergen Lacombe; Karsten von Maydell; Carsten Agert

We discuss an optical model which describes silicon thin-film solar cells with rough interfaces in a fast and easy way. In order to simulate thin layer stacks with rough interfaces diffuse scattering as well as interference effects have to be taken into account. Algorithms like the finite-difference time-domain method (FDTD) solve the Maxwell Equations, and therefore fulfil these demands; yet, they take a considerable amount of simulation time and computation capacity. To overcome these drawbacks, an optical model was developed which combines the transfer-matrix method (TMM) and the raytracer algorithm. The fraction of TMM and raytracer in the model is determined by a separating function which can be interpreted as the integral haze. In order to verify the combined optical model, a series of amorphous silicon single cells with varying intrinsic layer thicknesses was produced on two different kinds of textured substrates. The results of the combined optical model are compared to measured data and the simulation results of the FDTD method. We show that the combined optical model yields good results at low simulation time.

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Martin Vehse

University of Oldenburg

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Oleg Sergeev

University of Oldenburg

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R.-E. Nowak

University of Oldenburg

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