Neustadt an der Weinstraße, Germany
Neustadt an der Weinstraße, Germany

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Gerhard C.,HAWK University of Applied Sciences and Arts | Gerhard C.,Fraunhofer Institute for Surface Engineering and Thin Films | Weihs T.,HAWK University of Applied Sciences and Arts | Luca A.,Roth and Rau AG | And 3 more authors.
Journal of the European Optical Society | Year: 2013

In this paper, surface smoothing of optical glasses, glass ceramic and sapphire using a low-power dielectric barrier discharge inert gas plasma at atmospheric pressure is presented. For this low temperature treatment method, no vacuum devices or chemicals are required. It is shown that by such plasma treatment the micro roughness and waviness of the investigated polished surfaces were significantly decreased, resulting in a decrease in surface scattering. Further, plasma polishing of lapped fused silica is introduced. Based on simulation results, a plasma physical process is suggested to be the underlying mechanism for initialising the observed smoothing effect.

Laades A.,CiS Research Institute for Micro Sensors and Photovoltaics | Sperlich H.-P.,Roth and Rau AG | Bahr M.,CiS Research Institute for Micro Sensors and Photovoltaics | Sturzebecher U.,CiS Research Institute for Micro Sensors and Photovoltaics | And 5 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2012

The interface passivation of a -AlO x/a -SiN x:H stacks deposited on p-type silicon by plasma enhanced chemical vapor deposition is investigated by means of charge carrier lifetime and surface photovoltage measurements. To control the quality of the interface, we performed different surface preparation steps prior to a -AlO x/a -SiN x:H stack deposition. Our investigation is focussing on the interface passivation upon post-deposition thermal treatments such as annealing at 425 °C and firing as applied in the silicon solar cell industry. We demonstrate that the interface recombination is mainly controlled by the interface state density as demonstrated by lifetime and SPV measurements. The increase of the negative charge density after thermal steps as revealed by FTIR spectroscopy evidences that the field effect has at least an enhancing effect in improving the passivation level. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

To fflinger J.A.,Helmholtz Center Berlin | Laades A.,CiS Research Institute for Micro Sensors and Photovoltaics | Korte L.,Helmholtz Center Berlin | Leendertz C.,Helmholtz Center Berlin | And 4 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

The negative charge formation, the charge-trapping mechanisms and the interface defect passivation of aluminum oxide/silicon nitride (AlOx/SiNx) stacks deposited by plasma-enhanced chemical vapor deposition on p-type crystalline silicon (c-Si) are investigated. Constant voltage stress (CVS) investigations combined with capacitance-voltage (C-V) hysteresis analysis indicate the influence of different thermal treatments on the negative charge formation and allow discerning between fixed and trapped charges in the AlOx/SiNx system. The thermal budget during SiNx deposition activates negatively charged traps. An annealing step leads to the formation of a stable, fixed negative charge and reduces the defect state density (D it) at the c-Si/AlOx interface. A wet-chemical silicon oxidation (SiOx) of the c-Si surface reduces D it even further, but introduces additional traps at the wet-chemical SiOx/AlOx interface. These traps lead to instabilities of the negative charge density and have a detrimental effect on the passivation quality. However, a firing step leads to the formation of a higher negative charge density due to charged traps. Combined with the enhanced chemical passivation, this results in a higher passivation quality than upon annealing. The trap-related negative charge upon firing is unstable due to electron detrapping. However, a positive CVS can recharge traps in the wet-chemical SiOx/AlOx/SiNx system negatively through electron injection from the c-Si. © 2014 Elsevier B.V.

Linke D.,Leibniz Institute for Crystal Growth | Dropka N.,Leibniz Institute for Crystal Growth | Kiessling F.M.,Leibniz Institute for Crystal Growth | Konig M.,Roth and Rau AG | And 3 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

A 75 kg solar-grade boron-doped silicon (Si) ingot has been directionally solidified in a Vertical Gradient Freeze (VGF)-type G2-sized furnace equipped with KRISTMAG®Heater Magnet Module (HMM). Alternating Magnetic Fields (AMFs) were used to enhance melt stirring and to control the growth interface morphology and shape. This as-grown multicrystalline (mc)-silicon ingot of 384×384×230 mm3in volume was cut into 4 bricks and in Vertical Cuts (VC) to analyze the material and to produce solar cells. Numerical simulations have been performed in order to optimize mass transport processes. Information about the curvature of the liquid-solid interface, the distribution of carbon (C) and oxygen (O), the content of Silicon Carbide (SiC) and Silicon Nitride (Si3N4)-particles and the electrical activity of defects were obtained from the ingot core. Except for the last-to-freeze part, a primarily inclusion-free ingot was solidified. Minority carrier lifetimes of τ~4 μs were measured on the grinded as-cut surface. The concentrations of C and O were determined by Fourier Transform Infrared (FTIR) spectroscopy to (0.4-7.9)×1017atoms/cm3and (0.3-5.4)×1017atoms/cm3, respectively. Solar cells were produced from wafers at the Meyer Burger Roth & Rau Technology and Research Centre using the Meyer Burger Roth & Rau Passivated Emitter Rear Cell (PERC) process. Solar cell efficiencies were achieved between 17.7% and 18.0%. © 2014 Elsevier B.V.

Tofflinger J.A.,Helmholtz Center Berlin | Laades A.,CiS Forschungsinstitut FurMikrosensorik Und Photovoltaik GmbH | Leendertz C.,Helmholtz Center Berlin | Montanez L.M.,Helmholtz Center Berlin | And 4 more authors.
Energy Procedia | Year: 2014

The charge dynamics and the interface defect state density of AlOx/SiNx passivation stacks deposited by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) wafers are investigated. High frequency (1 MHz) capacitance voltage (C-V) measurements were performed on stacks in the as deposited state and after an annealing step. C-V sweeps reveal an initially high negative charge density for the as deposited sample, activated by the thermal budget during SiNx deposition. However, this charge state is unstable and reduced owning to electron detrapping and emission into the c-Si upon applying moderate voltages. In the annealed sample, the AlOx/SiNx stack has a stable negative fixed charge. Both for as deposited and for annealed samples, applying a positive or negative constant gate voltage stress (Vstress) enhances or reduces the negative effective charge density (Qox,eff), respectively. Injection of charges from the c-Si into traps in the AlOx/SiNx stack is identified as the mechanism responsible for this behavior. We conclude that in addition to fixed negative charges trapping of negative charges near the interface is a crucial mechanism contributing to the total effective negative charge of the stack. Their contribution depends on the temperature and duration of the thermal treatment. Additionally, a large Vstress leads to generation of additional Si dangling bond defects over the entire c-Si bang gap at the c-Si/AlOx interface. © 2014 The Authors. Published by Elsevier Ltd.

Zimmer K.,Leibniz Institute of Surface Modification | Bohme R.,Leibniz Institute of Surface Modification | Bohme R.,Roth and Rau AG | Ehrhardt M.,Leibniz Institute of Surface Modification | Rauschenbach B.,Leibniz Institute of Surface Modification
Applied Physics A: Materials Science and Processing | Year: 2010

In consequence of high interest in micro- and nanomachining of transparent materials by laser irradiation, studies on the mechanism of laser-induced backside wet etching (LIBWE) are presented. To reveal the role of the surface modification due to LIBWE the backside ablation (BSA) of LIBWE-modified fused silica (mFS) surfaces at 248 nm was investigated. The threshold fluence and the etch rate of BSA are similar to that of LIBWE and amount ∼250 mJ/cm 2 and 30 nm for 1 J/cm2, respectively. The sample transmission after backside ablation of mFS increases and proves the decreasing thickness of the absorbing layer. Time-resolved reflection studies at LIBWE and BSA of mFS show similar patterns in the backside reflection that can be assigned an ablation process as the comparison to thin polymer films demonstrates. By fitting the BSA data to an exponential decay absorption model a modification depth and a surface absorption of about 38 nm and α S ∼1.3×107 m-1 were calculated, respectively. In conclusion of the results a new model for LIBWE is proposed. © 2010 Springer-Verlag.

Siepchen B.,CTF Solar GmbH | Drost C.,CTF Solar GmbH | Spath B.,CTF Solar GmbH | Krishnakumar V.,CTF Solar GmbH | And 8 more authors.
Thin Solid Films | Year: 2013

CdTe is an attractive material to produce high efficient and low cost thin film solar cells. The semiconducting layers of this kind of solar cell can be deposited by the Close Spaced Sublimation (CSS) process. The advantages of this technique are high deposition rates and an excellent utilization of the raw material, leading to low production costs and competitive module prices. CTF Solar GmbH is offering equipment and process knowhow for the production of CdTe solar modules. For further improvement of the technology, research is done at a pilot line, which covers all relevant process steps for manufacture of CdTe solar cells. Herein, we present the latest results from the process development and our research activities on single functional layers as well as for complete solar cell devices. Efficiencies above 13% have already been obtained with Cu-free back contacts. An additional focus is set on different transparent conducting oxide materials for the front contact and a Sb2Te 3 based back contact. © 2012 Elsevier B.V.

Laades A.,CiS Research Institute for Micro Sensors and Photovoltaics | Sturzebecher U.,CiS Research Institute for Micro Sensors and Photovoltaics | Sperlich H.-P.,Roth and Rau AG | Moller C.,CiS Research Institute for Micro Sensors and Photovoltaics | And 2 more authors.
Solid State Phenomena | Year: 2014

We are investigating the effect of different wet chemical surface preconditioning sequences for silicon wafers prior to the deposition of aluminum oxide based passivation layers produced by plasma enhanced chemical vapor deposition. We are focusing on the development of a simple and industrially feasible preconditioning process to achieve a high level of interface passivation after the firing process applied to industrial solar cells. Our process optimization is monitored by characterizing the passivation quality before and after a firing process. We are also investigating the effectiveness of the removal of residual surface iron concentrations by the wet chemical process. © (2014) Trans Tech Publications, Switzerland.

Duttagupta S.,Solar Energy Research Institute of Singapore | Hameiri Z.,University of Sydney | Grosse T.,Roth and Rau AG | Landgraf D.,Roth and Rau AG | And 2 more authors.
IEEE Journal of Photovoltaics | Year: 2015

State-of-The-Art surface passivation results are obtained on undiffused p-Type commercial-grade Czochralski Si wafers with effective surface recombination velocity Seff values of ?8 cm/s and implied open-circuit voltage iVoc values of up to 715 mV with an industrially fired dielectric stack of silicon oxide and silicon nitride (SiOx/SiNx) deposited in an industrial inline plasma-enhanced chemical vapor deposition reactor. We are able to controllably vary the total positive charge density Qtotal in the stack by more than one order of magnitude (1011-1012 cm?2) with no impact on midgap interface state density Dit,midgap (5×1011 eV?1cm?2) by altering the deposition temperature of the SiOxlayer in the stack.We show experimentally that, for inversion conditions, Seff scales with the inverse square of the charge density 1/Q2 total , which is in good agreement with theory. Based on the measured injection-level-dependent minority carrier lifetimes and the total positive charge densities, it is shown that films with higher positive charge density have higher 1-sun Voc and fill factor (FF) potential. Large-Area alloyed aluminum local back surface field solar cells confirmed this by showing higher conversion efficiency by 0.17% absolute due to improved cell Voc and FF of the solar cells featuring a SiOx/SiNx stack with a higher Qtotal . © 2011-2012 IEEE.

Jurk R.,Fraunhofer Institute for Ceramic Technologies and Systems | Fritsch M.,Fraunhofer Institute for Ceramic Technologies and Systems | Eberstein M.,Fraunhofer Institute for Ceramic Technologies and Systems | Schilm J.,Fraunhofer Institute for Ceramic Technologies and Systems | And 3 more authors.
Journal of Micromechanics and Microengineering | Year: 2015

Ink jet printable water based inks are prepared by a new silver nanoparticle synthesis and the addition of nanoscaled ZnO particles. For the formation of front side contacts the inks are ink jet printed on the front side of micro crystalline silicon solar cells, and contact the cell directly during the firing step by etching through the wafers' anti-reflection coating (ARC). In terms of Ag dissolution and precipitation the mechanism of contact formation can be compared to commercial glass containing thick film pastes. This avoids additional processing steps, like laser ablation, which are usually necessary to open the ARC prior to ink jet printing. As a consequence process costs can be reduced. In order to optimize the ARC etching and contact formation during firing, zinc oxide nanoparticles are investigated as an ink additive. By utilization of in situ contact resistivity measurements the mechanism of contacting was explored. Our results show that silver inks containing ZnO particles realize a specific contact resistance below 10 mΩscm2. By using a multi-pass ink jet printing and plating process a front side metallization of commercial 6 × 6 inch2 standard micro crystalline silicone solar cells with emitter resistance of 60 Ω/ was achieved and showed an efficiency of 15.7%. © 2015 IOP Publishing Ltd.

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