TY  - GEN
A1  - Schulze, Patricia S. C.
A1  - Bett, Alexander J.
A1  - Bivour, Martin
A1  - Caprioglio, Pietro
A1  - Gerspacher, Fabian M.
A1  - Kabaklı, Özde Ş.
A1  - Richter, Armin
A1  - Stolterfoht, Martin
A1  - Zhang, Qinxin
A1  - Neher, Dieter
A1  - Hermle, Martin
A1  - Hillebrecht, Harald
A1  - Glunz, Stefan W.
A1  - Goldschmidt, Jan Christoph
T1  - 25.1% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80% and up to 25.1% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30% tandem efficiency in the near future.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1197 
KW  - heterojunction silicon solar cells
KW  - interfaces
KW  - perovskite solar cells
KW  - tandem solar cells
KW  - thin films
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525668
SN  - 1866-8372
IS  - 7
ER  - 
TY  - JOUR
A1  - Schulze, Patricia S. C.
A1  - Bett, Alexander J.
A1  - Bivour, Martin
A1  - Caprioglio, Pietro
A1  - Gerspacher, Fabian M.
A1  - Kabaklı, Özde Ş.
A1  - Richter, Armin
A1  - Stolterfoht, Martin
A1  - Zhang, Qinxin
A1  - Neher, Dieter
A1  - Hermle, Martin
A1  - Hillebrecht, Harald
A1  - Glunz, Stefan W.
A1  - Goldschmidt, Jan Christoph
T1  - 25.1% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber
JF  - Solar RRL
N2  - Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80% and up to 25.1% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30% tandem efficiency in the near future.
KW  - heterojunction silicon solar cells
KW  - interfaces
KW  - perovskite solar cells
KW  - tandem solar cells
KW  - thin films
Y1  - 2020
VL  - 4
IS  - 7
PB  - John Wiley & Sons, Inc.
CY  - New Jersey
ER  - 
TY  - JOUR
A1  - Assagra, Yuri A.O.
A1  - Altafim, Ruy Alberto Pisani
A1  - do Carmo, Joao P.
A1  - Altafim, Ruy A.C.
A1  - Rychkov, Dmitry
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - A new route to piezo-polymer transducers: 3D printing of polypropylene ferroelectrets
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Here, a promising approach for producing piezo-polymer transducers in a one-step process is presented. Using 3D-printing technology and polypropylene (PP) filaments, we are able to print a two-layered film structure with regular cavities of precisely controlled size and shape. It is found that the 3D-printed samples exhibit piezoelectric coefficients up to 200 pC/N, similar to those of other PP ferroelectrets, and their temporal and thermal behavior is in good agreement with those known of PP ferroelectrets. The piezoelectric response strongly decreases for applied pressures above 20 kPa, as the pressure in the air-filled cavities strongly influences the overall elastic modulus of ferroelectrets.
KW  - 3D printing
KW  - polymer ferroelectrets
KW  - sensors and actuators
KW  - piezoelectrets
KW  - electret polymers
KW  - soft electro-active materials
KW  - functional materials
KW  - soft matter
Y1  - 2020
U6  - https://doi.org/10.1109/TDEI.2020.008461
SN  - 1070-9878
SN  - 1558-4135
VL  - 27
IS  - 5
SP  - 1668
EP  - 1674
PB  - Inst. of Electr. and Electronics Engineers
CY  - Piscataway
ER  - 
TY  - JOUR
A1  - Gómez-Nava, Luis
A1  - Grossmann, Robert
A1  - Hintsche, Marius
A1  - Beta, Carsten
A1  - Peruani, Fernando
T1  - A novel approach to chemotaxis
BT  - active particles guided by internal clocks
JF  - epl : a letters journal exploring the frontiers of physics
N2  - Motivated by the observation of non-exponential run-time distributions of bacterial swimmers, we propose a minimal phenomenological model for taxis of active particles whose motion is controlled by an internal clock. The ticking of the clock depends on an external concentration field, e.g., a chemical substance. We demonstrate that these particles can detect concentration gradients and respond to them by moving up- or down-gradient depending on the clock design, albeit measurements of these fields are purely local in space and instantaneous in time. Altogether, our results open a new route in the study of directional navigation: we show that the use of a clock to control motility actions represents a generic and versatile toolbox to engineer behavioral responses to external cues, such as light, chemical, or temperature gradients.
Y1  - 2020
U6  - https://doi.org/10.1209/0295-5075/130/68002
SN  - 0295-5075
SN  - 1286-4854
VL  - 130
IS  - 6
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Gostkowska-Lekner, Natalia Katarzyna
A1  - Wallacher, Dirk
A1  - Grimm, Nico
A1  - Habicht, Klaus
A1  - Hofmann, Tommy
T1  - A novel electrochemical anodization cell for the synthesis of mesoporous silicon
JF  - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques
N2  - A novel design of an electrochemical anodization cell dedicated to the synthesis of mesoporous, single-crystalline silicon is presented. First and foremost, the design principle follows user safety since electrochemical etching of silicon requires highly hazardous electrolytes based on hydrofluoric (HF) acid. The novel cell design allows for safe electrolyte handling prior, during, and post-etching. A peristaltic pump with HF-resistant fluoroelastomer tubing transfers electrolytes between dedicated reservoirs and the anodization cell. Due to the flexibility of the cell operation, different processing conditions can be realized providing a large parameter range for the attainable sample thickness, its porosity, and the mean pore size. Rapid etching on the order of several minutes to synthesize micrometer-thick porous silicon epilayers on bulk silicon is possible as well as long-time etching with continuous, controlled electrolyte flow for several days to prepare up to 1000 mu m thick self-supporting porous silicon membranes. A highly adaptable, LabVIEW((TM))-based control software allows for user-defined etching profiles.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0008536
SN  - 0034-6748
SN  - 1089-7623
VL  - 91
IS  - 10
PB  - American Institute of Physics
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Großmann, Robert
A1  - Aranson, Igor S.
A1  - Peruani, Fernando
T1  - A particle-field approach bridges phase separation and collective motion in active matter
JF  - Nature Communications
N2  - Whereas self-propelled hard discs undergo motility-induced phase separation, self-propelled rods exhibit a variety of nonequilibrium phenomena, including clustering, collective motion, and spatio-temporal chaos. In this work, we present a theoretical framework representing active particles by continuum fields. This concept combines the simplicity of alignment-based models, enabling analytical studies, and realistic models that incorporate the shape of self-propelled objects explicitly. By varying particle shape from circular to ellipsoidal, we show how nonequilibrium stresses acting among self-propelled rods destabilize motility-induced phase separation and facilitate orientational ordering, thereby connecting the realms of scalar and vectorial active matter. Though the interaction potential is strictly apolar, both, polar and nematic order may emerge and even coexist. Accordingly, the symmetry of ordered states is a dynamical property in active matter. The presented framework may represent various systems including bacterial colonies, cytoskeletal extracts, or shaken granular media. Interacting self-propelled particles exhibit phase separation or collective motion depending on particle shape. A unified theory connecting these paradigms represents a major challenge in active matter, which the authors address here by modeling active particles as continuum fields.
Y1  - 2020
U6  - https://doi.org/10.1038/s41467-020-18978-5
SN  - 2041-1723
VL  - 11
IS  - 1
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Schaffenroth, Veronika
A1  - Casewell, Sarah L.
A1  - Schneider, D.
A1  - Kilkenny, David
A1  - Geier, Stephan
A1  - Heber, Ulrich
A1  - Irrgang, Andreas
A1  - Przybilla, Norbert
A1  - Marsh, Thomas R.
A1  - Littlefair, Stuart P.
A1  - Dhillon, Vik S.
T1  - A quantitative in-depth analysis of the prototype sdB plus BD system SDSS J08205+0008 revisited in the Gaia era
JF  - Monthly notices of the Royal Astronomical Society
N2  - Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) x 10(-12) dd(-1). This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of 0.39-0.50 M-circle dot and a radius of R-sdB = 0.194 +/- 0.008 R-circle dot, and the companion to 0.061-0.071 M-circle dot with a radius of R-comp = 0.092 +/- 0.005 R-circle dot, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf.
KW  - stars: abundances
KW  - stars: atmospheres
KW  - stars: fundamental parameters
KW  - stars: horizontal branch
KW  - stars: low-mass
KW  - subdwarfs
Y1  - 2020
U6  - https://doi.org/10.1093/mnras/staa3661
SN  - 0035-8711
SN  - 1365-2966
VL  - 501
IS  - 3
SP  - 3847
EP  - 3870
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Sajedi, Maryam
A1  - Krivenkov, Maxim
A1  - Marchenko, Dmitry
A1  - Varykhalov, Andrei
A1  - Sanchez-Barriga, Jaime
A1  - Rienks, Emile D. L.
A1  - Rader, Oliver
T1  - Absence of a giant Rashba effect in the valence band of lead halide perovskites
JF  - Physical review : B, Condensed matter and materials physics
N2  - For hybrid organic-inorganic as well as all-inorganic lead halide perovskites a Rashba effect has been invoked to explain the high efficiency in energy conversion by prohibiting direct recombination. Both a bulk and surface Rashba effect have been predicted. In the valence band of methylammonium (MA) lead bromide a Rashba effect has been reported by angle-resolved photoemission and circular dichroism with giant values of 7-11 eV angstrom. We present band dispersion measurements of MAPbBr(3) and spin-resolved photoemission of CsPbBr3 to show that a large Rashba effect detectable by photoemission or circular dichroism does not exist and cannot be the origin of the high effciency.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevB.102.081116
SN  - 2469-9950
SN  - 2469-9969
VL  - 102
IS  - 8
PB  - American Institute of Physics; American Physical Society (APS)
CY  - Woodbury, NY
ER  - 
TY  - JOUR
A1  - Umlandt, Maren
A1  - Feldmann, David
A1  - Schneck, Emanuel
A1  - Santer, Svetlana
A1  - Bekir, Marek
T1  - Adsorption of photoresponsive surfactants at solid-liquid interfaces
JF  - Langmuir
N2  - We report on the adsorption kinetics of azoben-zene-containing surfactants on solid surfaces of different hydrophobicity. The understanding of this processes is of great importance for many interfacial phenomena that can be actuated and triggered by light, since the surfactant molecules contain a photoresponsive azobenzene group in their hydrophobic tail. Three surfactant types are studied, differing in the spacer connecting the headgroup and the azobenzene unit by between 6 and 10 CH2 groups. Under irradiation with light of a suitable wavelength, the azobenzene undergoes reversible photoisomerization between two states, a nonpolar trans-state and a highly polar cis-state. Consequently, the surfactant molecule changes its hydrophobicity and thus affinity to a surface depending on the photoisomerization state of the azobenzene. The adsorption behavior on hydrophilic (glass) and hydrophobic (TeflonAF) surfaces is analyzed using quartz crystal microbalance with dissipation (QCM-D) and zeta-potential measurements. At equilibrium, the adsorbed surfactant amount is almost twice as large on glass compared to TeflonAF for both isomers. The adsorption rate for the trans-isomers on both surfaces is similar, but the desorption rate of the trans-isomers is faster at the glass-water interface than at the Teflon-water interface. This result demonstrates that the trans-isomers have higher affinity for the glass surface, so the trans-to-cis ratios on glass and TeflonAF are 80/1 and 2/1, respectively, with similar trends for all three surfactant types.
Y1  - 2020
U6  - https://doi.org/10.1021/acs.langmuir.0c02545
SN  - 0743-7463
SN  - 1520-5827
VL  - 36
IS  - 46
SP  - 14009
EP  - 14018
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Evsevleev, Sergei
A1  - Paciornik, Sidnei
A1  - Bruno, Giovanni
T1  - Advanced deep learning-based 3D microstructural characterization of multiphase metal matrix composites
JF  - Advanced engineering materials
N2  - The quantitative analysis of microstructural features is a key to understanding the micromechanical behavior of metal matrix composites (MMCs), which is a premise for their use in practice. Herein, a 3D microstructural characterization of a five-phase MMC is performed by synchrotron X-ray computed tomography (SXCT). A workflow for advanced deep learning-based segmentation of all individual phases in SXCT data is shown using a fully convolutional neural network with U-net architecture. High segmentation accuracy is achieved with a small amount of training data. This enables extracting unprecedently precise microstructural parameters (e.g., volume fractions and particle shapes) to be input, e.g., in micromechanical models.
KW  - computed tomography
KW  - convolutional neural networks
KW  - deep learning
KW  - metal
KW  - matrix composites
KW  - segmentations
Y1  - 2020
U6  - https://doi.org/10.1002/adem.201901197
SN  - 1438-1656
SN  - 1527-2648
VL  - 22
IS  - 4
PB  - Wiley-VCH
CY  - Weinheim
ER  -