Florian Ruske
@helmholtz-berlin.de
Novel Materials and interfaces for photovoltaic solar cells
Helmholtz-Zentrum Berlin
RESEARCH, TEACHING, or OTHER INTERESTS
Surfaces, Coatings and Films, Renewable Energy, Sustainability and the Environment, Electronic, Optical and Magnetic Materials
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Victor Ukleev, Ludmila Leroy, Riccardo Mincigrucci, Dario De Angelis, Danny Fainozzi, Nupur Ninad Khatu, Ettore Paltanin, Laura Foglia, Filippo Bencivenga, Chen Luo,et al.
AIP Publishing
Surface acoustic waves (SAWs) are excited by femtosecond extreme ultraviolet (EUV) transient gratings (TGs) in a room-temperature ferrimagnetic DyCo5 alloy. TGs are generated by crossing a pair of EUV pulses from a free electron laser with the wavelength of 20.8 nm matching the Co M-edge, resulting in a SAW wavelength of Λ = 44 nm. Using the pump-probe transient grating scheme in reflection geometry, the excited SAWs could be followed in the time range of −10 to 100 ps in the thin film. Coherent generation of TGs by ultrafast EUV pulses allows to excite SAW in any material and to investigate their couplings to other dynamics, such as spin waves and orbital dynamics. In contrast, we encountered challenges in detecting electronic and magnetic signals, potentially due to the dominance of the larger SAW signal and the weakened reflection signal from underlying layers. A potential solution for the latter challenge involves employing soft x-ray probes, albeit introducing additional complexities associated with the required grazing incidence geometry.
David Stock, Nikolaus Weinberger, Florian Ruske, Leander Haug, Martina Harnisch, and Roman Lackner
Elsevier BV
I Kafedjiska, G Farias Basulto, F Ruske, N Maticiuc, T Bertram, C A Kaufmann, R Schlatmann, and I Lauermann
IOP Publishing
Abstract We present monolithic copper–indium–gallium–diselenide (Cu(In,Ga)Se2, CIGSe)-perovskite tandem solar cells with air- or N2-transferred NiO x :Cu with or without self-assembled monolayer (SAM) as a hole-transporting layer (HTL). A champion efficiency of 23.2%, open-circuit voltage (V o c ) of 1.69 V, and a fill factor (FF) of 78.3% are achieved for the tandem with N2-transferred NiO x :Cu + SAM. The samples with air-transferred NiO x :Cu + SAM have V o c and FF losses, while those without SAM are heavily shunted. We find via x-ray and UV photoelectron spectroscopy that the air exposure leads to non-negligible loss in the Ni2+ species and changes in the NiO x :Cu’s work function and valence band maxima, both of which can negatively impact the V o c and the FF of the tandems. Furthermore, by performing dark lock-in thermography, photoluminescence (PL), and scanning electron microscopy studies, we are able to detect various morphological defects in the tandems with poor performance, such as ohmic shunts originating from defects in the bottom CIGSe cell, or from cracking/delaminating of the perovskite top cell. Finally, by correlating the detected shunts in the tandems with PL-probed bottom device, we can conclude that not all defects in the bottom device induce ohmic shunts in the tandems since the NiO x :Cu + SAM HTL bi-layer can decouple the growth of the top device from the rough, defect-rich and defect-tolerant bottom device and enable high-performing devices.
Marlene Härtel, Bor Li, Silvia Mariotti, Philipp Wagner, Florian Ruske, Steve Albrecht, and Bernd Szyszka
Elsevier BV
Ke Xu, Amran Al-Ashouri, Zih-Wei Peng, Eike Köhnen, Hannes Hempel, Fatima Akhundova, Jose A. Marquez, Philipp Tockhorn, Oleksandra Shargaieva, Florian Ruske,et al.
American Chemical Society (ACS)
Wide bandgap halide perovskite materials show promising potential to pair with silicon bottom cells. To date, most efficient wide bandgap perovskites layers are fabricated by spin-coating, which is difficult to scale up. Here, we report on slot-die coating for an efficient, 1.68 eV wide bandgap triple-halide (3halide) perovskite absorber, (Cs0.22FA0.78)Pb(I0.85Br0.15)3 + 5 mol % MAPbCl3. A suitable solvent system is designed specifically for the slot-die coating technique. We demonstrate that our fabrication route is suitable for tandem solar cells without phase segregation. The slot-die coated wet halide perovskite is dried by a “nitrogen (N2)-knife” with high reproducibility and avoiding antisolvents. We explore varying annealing conditions and identify parameters allowing crystallization of the perovskite film into large grains reducing charge collection losses and enabling higher current density. At 150 °C, an optimized trade-off between crystallization and the PbI2 aggregates on the film’s top surface is found. Thus, we improve the cell stability and performance of both single-junction cells and tandems. Combining the 3halide top cells with a 120 μm thin saw damage etched commercial Czochralski industrial wafer, a 2-terminal monolithic tandem solar cell with a PCE of 25.2% on a 1 cm2 active area is demonstrated with fully scalable processes.
Engin Özkol, Philipp Wagner, Florian Ruske, Bernd Stannowski, and Lars Korte
Wiley
To increase the efficiency in p‐type wafer‐based silicon heterojunction (SHJ) technology, one of the most crucial challenges is the achievement of excellent surface passivation. Herein, chemical passivation techniques known for n‐type technology are successfully applied on p‐type float–zone (FZ) wafers, and wafer surface passivation quality is correlated with parameters from plasma diagnostics, namely crystallization rate and electron temperature indices. It is shown that plasma ignition at higher powers than deposition powers enhances effective minority carrier lifetimes τeff fourfold for p‐ (0.6–2.1 ms) and sixfold for n‐type (0.6–3.2 ms) wafers while giving opportunity to process under lower electron temperature indices during the nucleation phase. A subsequent hydrogen plasma treatment has a further beneficial effect on chemical passivation, leading to high effective minority carrier lifetimes of 4.5 and 3.1 ms, and implies open‐circuit voltages, i‐VOC, of 735 and 720 mV for p‐ and n‐type wafers, respectively. In particular, cell precursors built on p‐type wafers demonstrate excellent surface passivation with τeff and i‐VOC (4.1 ms and 745 mV). Using these process optimizations, SHJ cells on both p‐ and n‐type wafers are fabricated with efficiencies exceeding 21%.
Alexandros Cruz, Darja Erfurt, Philipp Wagner, Anna B. Morales-Vilches, Florian Ruske, Rutger Schlatmann, and Bernd Stannowski
Elsevier BV
Alvaro Tejada, Sven Peters, Amran Al‐Ashouri, Silver Hamill Turren‐Cruz, Antonio Abate, Steve Albrecht, Florian Ruske, Bernd Rech, Jorge Andrés Guerra, and Lars Korte
Wiley
AbstractA quantitative analysis of the thermally induced degradation of various device‐relevant multi‐cation hybrid perovskite films is performed using spectroscopic ellipsometry, for temperatures between 80 and 120 °C. The studied compositions are a triple cation perovskite Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3, a Rb‐containing variant Rb0.05Cs0.05(MA0.17FA0.83)0.90Pb(Br0.17I0.83)3, and a methylammonium‐free Rb0.05Cs0.10FA0.85PbI3 composition. A very wide combined spectral range of 200 nm to 25 μm is covered by combining the data from two separate instruments. The relative changes in organic cation concentrations are quantified from the middle infrared molecular absorption bands, leveraging the use of point‐by‐point fitting for increased sensitivity. Additionally, the formation of PbI2 and non‐perovskite δ‐CsPbI3 phases is evidenced from Bruggemann effective medium fits to the visible and ultraviolet complex refractive indices. Methylammonium is almost completely depleted from the relevant compositions within 100 to 285 min of thermal annealing. The MA‐free perovskite degrades faster at intermediate temperatures, which is attributed to phase instability due to the formation of δ‐CsPbI3 in addition to PbI2.
Hasan A. Yetkin, Tim Kodalle, Tobias Bertram, Alejandra Villanueva Tovar, Reiner Klenk, Marin Rusu, Josefa Ibaceta-Jana, Florian Ruske, Ibrahim Simsek, Ruslan Muydinov,et al.
Institute of Electrical and Electronics Engineers (IEEE)
In this contribution, the impact of thermal stress on Cu(In,Ga)Se<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> (CIGSe) thin film photovoltaic devices is investigated. The tolerance of such devices to high temperatures is of particular interest for processing transparent conductive oxides (TCOs) in order to further close the gap to the theoretical efficiency limit and for their potential use as bottom devices in tandem applications in order to overcome the theoretical efficiency limit of single junction solar cells. When CdS-buffered CIGSe high efficiency solar cells are subjected to thermal stress, elemental interdiffusion of Na and Cd between the absorber and the window layers as well as chemical reactions at the CIGSe/CdS interface result in a degraded power conversion efficiency (PCE). Here, we compare the degradation mechanisms of CdS and GaO<inline-formula><tex-math notation="LaTeX">$_{x}$</tex-math></inline-formula> buffered CIGSe solar cells under thermal stress. A model explaining the observed degradation behaviors is proposed.
Jens Niederhausen, Rowan W. MacQueen, Engin Özkol, Clemens Gersmann, Moritz H. Futscher, Martin Liebhaber, Dennis Friedrich, Mario Borgwardt, Katherine A. Mazzio, Patrick Amsalem,et al.
American Chemical Society (ACS)
The rational combination of tetracene (Tc) with crystalline silicon (c-Si) could greatly enhance c-Si solar cell efficiencies via singlet fission. The Tc/c-Si energy-level alignment (ELA) is though...
Alexandros Cruz, Florian Ruske, Alberto Eljarrat, Pawel P. Michalowski, Anna B. Morales-Vilches, Sebastian Neubert, Er-Chien Wang, Christoph T. Koch, Bernd Szyszka, Rutger Schlatmann,et al.
Institute of Electrical and Electronics Engineers (IEEE)
In this article, we report on the properties of indium tin oxide (ITO) deposited on thin-film silicon layers designed for the application as carrier selective contacts for silicon heterojunction (SHJ) solar cells. We find that ITO deposited on hydrogenated nanocrystalline silicon (nc-Si:H) layers presents a significant drop on electron mobility <inline-formula><tex-math notation="LaTeX">${\\mu} _{{\\rm{e}}}$</tex-math></inline-formula> in comparison to layers deposited on hydrogenated amorphous silicon films (a-Si:H). The nc-Si:H layers are not only found to exhibit a larger crystallinity than a-Si:H, but are also characterized by a considerably increased surface rms roughness. As we can see from transmission electron microscopy (TEM), this promotes the growth of smaller and fractured features in the initial stages of ITO growth. Furthermore, secondary ion mass spectrometry profiles show different penetration depths of hydrogen from the thin film silicon layers into the ITO, which might both influence ITO and device passivation properties. Comparing ITO to aluminum doped zinc oxide (AZO), we find that AZO can actually exhibit superior properties on nc-Si:H layers. We assess the impact of the modified ITO <italic>R</italic><sub>sh</sub> on the series resistance <inline-formula><tex-math notation="LaTeX">$R_{s}$</tex-math></inline-formula> of SHJ solar cells with >23% efficiency for optimized devices. This behavior should be considered when designing solar cells with amorphous or nanocrystalline layers as carrier selective contacts.
M.D. Heinemann, F. Ruske, D. Greiner, A.R. Jeong, M. Rusu, B. Rech, R. Schlatmann, and C.A. Kaufmann
Elsevier BV
H. Scherg-Kurmes, S. Körner, S. Ring, M. Klaus, L. Korte, F. Ruske, R. Schlatmann, B. Rech, and B. Szyszka
Elsevier BV
R. Muydinov, A. Steigert, S. Schönau, F. Ruske, R. Kraehnert, B. Eckhardt, I. Lauermann, and B. Szyszka
Elsevier BV
R. Muydinov, F. Ruske, S. Neubert, A. Steigert, M. Klaus, S. Selve, G. Köppel, and B. Szyszka
Elsevier BV
Sven Ring, Sebastian Neubert, Christof Schultz, Sebastian S. Schmidt, Florian Ruske, Bernd Stannowski, Frank Fink, and Rutger Schlatmann
Wiley
We present a‐Si:H/µc‐Si:H tandem solar cells on laser textured ZnO:Al front contact layers. Direct pulsed laser interference patterning (DLIP) was used for writing arrays of one‐dimensional micro gratings of submicron period into ZnO:Al films. The laser texture provides good light trapping which is indicated by an increase in short‐circuit current density of 20% of the bottom cell limited device compared to cells on planar ZnO:Al. The open‐circuit voltage of the cells on laser textured ZnO:Al is almost the same as for cells on planar substrates, indicating excellent growth conditions for amorphous and microcrystalline silicon on the U‐shaped grating grooves. DLIP is a simple, single step and industrially applicable method for large area periodic texturing of ZnO:Al thin films. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)
Sebastian Neubert, Mark Wimmer, Florian Ruske, Sonya Calnan, Onno Gabriel, Bernd Stannowski, Rutger Schlatmann, and Bernd Rech
Wiley
ABSTRACTIn recent years, zinc oxide has been investigated as a front electrode material in hydrogenated amorphous silicon/hydrogenated microcrystalline silicon (a‐Si:H/µc‐Si:H) tandem solar cells. Such as for other transparent conducting oxide materials and applications, a proper balancing of transparency and conductivity is necessary. The latter is directly related to the density and the mobility of charge carriers. A high density of charge carriers increases conductivity but leads to a higher absorption of light in the near‐infrared part of the spectrum due to increased free‐carrier absorption. Hence, the only way to achieve high conductivity while keeping the transparency as high as possible relies on an increase of carrier mobility. The carrier density and the mobility of sputtered Al‐doped zinc oxide (ZnO:Al) can be tailored by a sequence of different annealing steps. In this work, we implemented such annealed ZnO:Al films as a front electrode in a‐Si:H/µc‐Si:H tandem solar cells and compared the results with those of reference cells grown on as‐deposited ZnO:Al. We observed an improvement of short‐circuit current density as well as open‐circuit voltage and fill factor. The gain in current density could be attributed to a reduction of both sub‐band‐gap absorption and free‐carrier absorption in the ZnO:Al. The higher open‐circuit voltage and fill factor are indicators of a better device quality of the silicon for cells grown on annealed ZnO:Al. Altogether, the annealing led to an improved initial conversion efficiency of 12.1%, which was a gain of +0.7% in absolute terms. Copyright © 2013 John Wiley & Sons, Ltd.
D. Gerlach, M. Wimmer, R. G. Wilks, R. Félix, F. Kronast, F. Ruske, and M. Bär
Royal Society of Chemistry (RSC)
The interface between solid-phase crystallized phosphorous-doped polycrystalline silicon (poly-Si(n(+))) and aluminum-doped zinc oxide (ZnO:Al) was investigated using spatially resolved photoelectron emission microscopy. We find the accumulation of aluminum in the proximity of the interface. Based on a detailed photoemission line analysis, we also suggest the formation of an interface species. Silicon suboxide and/or dehydrated hemimorphite have been identified as likely candidates. For each scenario a detailed chemical reaction pathway is suggested. The chemical instability of the poly-Si(n(+))/ZnO:Al interface is explained by the fact that SiO2 is more stable than ZnO and/or that H2 is released from the initially deposited a-Si:H during the crystallization process. As a result, Zn (a deep acceptor in silicon) is "liberated" close to the silicon/zinc oxide interface presenting the inherent risk of forming deep defects in the silicon absorber. These could act as recombination centers and thus limit the performance of silicon/zinc oxide based solar cells. Based on this insight some recommendations with respect to solar cell design, material selection, and process parameters are given for further knowledge-based thin-film silicon device optimization.
S. Schönau, F. Ruske, S. Neubert, and B. Rech
Wiley
AbstractIn order to clarify the origin of the previously reported reduction of sub‐band gap absorption of sputtered ZnO:Al films upon thermal annealing and raising deposition temperature, structural characterization using Ra‐man spectroscopy was carried out on various films. Correlation of the Urbach energy to the FWHM of the E(high)2 mode was found. Oxygen addition to the film growth did not result in changes of the Urbach energy, despite pronounced changes of the electrical properties. The results suggest that extended defects, rather than intrinsic point defects, give rise to the sub‐band gap absorption. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carolin Zachäus, Christiane Becker, Florian Ruske, and Bernd Rech
Elsevier BV
Tobias Sontheimer, Daniel Amkreutz, Katharina Schulz, Paul H. Wöbkenberg, Christian Guenther, Vadym Bakumov, Joachim Erz, Christoph Mader, Stephan Traut, Florian Ruske,et al.
Wiley
Dr. T. Sontheimer, Dr. D. Amkreutz, Dr. F. Ruske, Dr. M. Weizman, Dr. A. Schnegg, Prof. Dr. B. Rech Helmholtz Zentrum Berlin Silicon Photovoltaics Kekuléstr. 5 , Berlin 12489 , Germany E-mail: tobias.sontheimer@helmholtz-berlin.de K. Schulz, Dr. P. H. Wöbkenberg, C. Guenther, Dr. V. Bakumov, J. Erz, Dr. C. Mader, Dr. S. Traut, Dr. M. Patz, Dr. M. Trocha, Dr. O. Wunnicke Evonik Industries AG Paul-Baumann Str. 1 , Marl 45772 , Germany
D. Amkreutz, J. Haschke, T. Häring, F. Ruske, and B. Rech
Elsevier BV
J. Hüpkes, J.I. Owen, M. Wimmer, F. Ruske, D. Greiner, R. Klenk, U. Zastrow, and J. Hotovy
Elsevier BV
B. Stannowski, F. Ruske, S. Neubert, S. Schönau, S. Ring, S. Calnan, M. Wimmer, O. Gabriel, B. Szyszka, B. Rech,et al.
Elsevier BV
Steffi Schönau, Florian Ruske, Sebastian Neubert, and Bernd Rech
Springer Science and Business Media LLC
ABSTRACTThin films of pure aluminum doped ZnO and with addition of nitrogen, oxygen and hydrogen have been prepared by magnetron sputtering. The spectral absorption coefficient close to the band gap energy has been determined by spectrophotometry and analyzed regarding band tailing and creation of defect bands. We found, that an improvement of Raman crystallinity under O2- rich growth conditions is not accompanied by a suppression of band tailing as expected. An additional absorption feature evolves for layers grown in N2 containing atmosphere. Doping with hydrogen attenuates sub-band gap absorption.