TY - THES
A1 - Brose, Robert
T1 - From dawn till dusk
BT - modelling particle acceleration in supernova remnants
N2 - Supernova remnants are believed to be the source of cosmic rays with energies up to 10^15 eV that are produced within our Galaxy. The acceleration mechanism associated with the collision-less shocks in supernova remnants - diffusive shock acceleration - predicts a spectral index of the accelerated non-thermal particles of s = 2. However, measurements of non-thermal emission in radio, X-rays and gamma-rays reveal significant deviations of the particles spectral index from the canonical value of s = 2.
The youngest Galactic supernova remnant G1.9+0.3 is an interesting target for next-generation gamma-ray observatories. So far, the remnant is only detected in the radio and the X-ray bands, but its young age of ≈100 yrs and inferred shock speed of ≈ 14, 000 km/s could make it an efficient particle accelerator.
I performed spherical symmetric 1D simulations with the RATPaC code, in which I simultaneously solved the transport equation for cosmic rays, the transport equation for magnetic turbulence, and the hydro-dynamical equations for the gas flow. Separately computed distributions of the particles accelerated at the forward and the reverse shock were then used to calculate the spectra of synchrotron, inverse Compton, and Pion-decay radiation from the source.
The emission from G1.9+0.3 can be self-consistently explained within the test-particle limit. I find that the X-ray flux is dominated by emission from the forward shock while most of the radio emission originates near the reverse shock, which makes G1.9+0.3 the first remnant with non-thermal radiation detected from the reverse shock. The flux of very-high-energy gamma-ray emission from G1.9+0.3 is expected to be close to the sensitivity threshold of the Cherenkov Telescope Array. The limited time available to grow large-scale turbulence limits the maximum energy of particles to values below 100 TeV, hence G1.9+0.3 is not a PeVatron.
Although there are many models for the acceleration of cosmic rays in Supernova remnants, the escape of cosmic rays from these sources is yet understudied.
I use our time-dependent acceleration code RATPaC to study the acceleration of cosmic rays and their escape in post-adiabatic Supernova remnants and calculate the subsequent gamma-ray emission from inverse-Compton scattering and Pion decay. My simulations span 100,000 years, thus covering the free-expansion, the Sedov-Taylor, and the beginning of the post-adiabatic phase of the remnant’s evolution.
At later stages of the evolution cosmic rays over a wide range of energy can reside outside of the remnant, creating spectra that are softer than predicted by standard diffusive shock acceleration and feature breaks in the 10 - 100 GeV-range. The total spectrum of cosmic rays released into the interstellar medium has a spectral index of s ≈ 2.4 above roughly 10 GeV which is close to that required by Galactic propagation models. I further find the gamma-ray luminosity to peak around an age of 4,000 years for inverse-Compton-dominated high-energy emission. Remnants expanding in low-density media emit generally more inverse-Compton radiation matching the fact that the brightest known supernova remnants - RCW86, Vela Jr, HESSJ1721-347 and RXJ1713.7-3946 - are all expanding in low density environments.
The importance of feedback from the cosmic-rays on the hydrodynamical evolution of the remnants is debated as a possibility to obtain soft cosmic-ray spectra at low energies.
I performed spherically symmetric 1-D simulations with a modified version of the RATPaC code, in which I simultaneously solve the transport equation for cosmic rays and the hydrodynamical equations, including the back-reaction of the cosmic-ray pressure on the flow profiles.
Besides the known modification of the flow profiles and the consequently curved cosmic-ray spectra, steady-state models for non-linear diffusive shock acceleration overpredict the total compression ratio that can be reached with cosmic-ray feedback, as there is limited time for building these modifications. Further, I find modifications to the downstream flow structure that change the evolutionary behavior of the remnant and trigger a cosmic-ray-induced instability close to the contact discontinuity, if and when the cosmic-ray pressure becomes dominant there.
N2 - Es wird vermutet das Supernovaüberreste die Quelle der galaktischen kosmischen Strahlung mit Energien bis zu 10^15eV sein können. Der Beschleunigungsprozess der mit den kollisionsfreien Schocks in Supernovaüberresten in Verbindung gebracht wird - diffuse Schockwellenbeschleunigung - sagt nicht-thermische Teilchenspektren mit einem Spektralindex von s=2 voraus. Messungen nicht-thermischer Strahlung im Radio-, Röntgen- und Gammastrahlenbereich zeigen teils deutliche Abweichungen von dieser Vorhersage.
Der jüngste galaktische Supernovaüberrest G1.9+0.3 ist ein interessantes Ziel für zukünftige Gammastrahlenteleskope. Bis jetzt wurde der Überrest nur im Radio- und Röntgenband entdeckt aber sein geringes Alter von ~100 Jahren und die gemessenen hohen Schockgeschwindigkeiten von ~14,000km/s sollten Teilchenbeschleunigung auch bis zu sehr hohen Energien ermöglichen.
In dieser Arbeit wurden 1D-Simulationen der Teilchenbeschleunigung in G1.9+0.3 mit Hilfe der RATPaC-Programmbibliothek durchgeführt, wobei das System der gekoppelten Differentialgleichungen für den Teilchentransport, den Transport der magnetischen Turbulenz und der Standardgasgleichungen gelöst wurde. Die separat berechneten Verteilungen der Teilchen an Vorwärts- und Rückwärtsschock wurden benutzt um die Emission des Überrests im Radio-, Röntgen und Gammastrahlungsbereich zu bestimmen.
Die Emissionen von G1.9+0.3 können selbst konsistent in der Testteilchennäherung bestimmt werden. Die Röntgenemission wird vom Vorwärtsschock dominiert, während die Radioemissionen hauptsächlich vom Rückwätsschock stammen. Dies macht G1.9+0.3 zum ersten Überrest mit detektierter nich-thermischer Strahlung aus dem Bereich des Rückwärtsschocks. Die erwartet Gammastrahlungsemission ist nahe dem Detektionslimit des zukünftigen Cherenkov Telescope Arrays. Die geringe Alter von G1.9+0.3 begrenzt die Maximalenergie, die im Beschleunigungsprozess erreicht werden kann auf Werte unterhalb von 100TeV. Demnach ist G1.9+0.3 kein PeVatron.
Auch wenn es zahlreiche Modelle zur Teilchenbeschleunigung in Supernovaüberresten gibt, ist das Entkommen der Teilchen aus den Überresten zur Zeit wenig erforscht.
Mit Hilfe von RATPaC haben wir die Evolution und Teilchenbeschleunigung in Supernovaüberresten über 100,000 Jahre simuliert. Dieser Zeitraum deckt einen Großteil der Lebensspanne eines Supernovaüberrests ab und endet mit der letzten Teil der postadiabatischen Phase der Entwicklung des Überrests.
In den späten Phasen der Entwicklung des Überrests können Teilchen in einem großen Energiebereich aus dem Überrest entweichen. Dies erzeugt Emissionspektren, die weicher sind als durch Fermibeschleunigung vorhergesagt, und die spektrale Brüche im Bereich von 10-100GeV aufweisen. Das Produktionsspektren der Überreste hat einen spektralen Index von s~2.4 oberhalb von 10GeV, was ungefähr mit den Spektren übereinstimmt, die Quellen in galaktischen Propagationsmodellen aufweisen müssen. Weiterhin erreichen die Überreste ihre größte Helligkeit im Gammabereich nach etwa 4000 Jahren wenn diese durch inverse Comptonstreuung erzeugt werden. Dabei erreichen Überreste in Medien mit geringer Umgebungsdichte größere Helligkeiten, was sich mit den Beobachtungen der hellsten Supernovaüberreste - RCW86, Vela Jr., HESSJ1721-347 und RXJ1713.7-3946 - deckt, die alle in Bereichen sehr geringer Umgebungsdichte expandieren.
In der Literatur wird die Möglichkeit diskutiert, dass die Rückkopplung der Beschleunigten Teilchen auf die Struktur der Überreste für die beobachteten weichen Strahlungsspektren verantwortlich ist.
Im Rahmen dieser Arbeit wurde eine modifizierte Version von RATPaC entwickelt, die diesen Prozess abbilden kann.
Neben den bekannten Rückkopplungen zeigt sich, dass bisherige Modelle unter der Annahme eines Gleichgewichtszustandes für die beschleunigten Teilchen die erreicht maximal Kompression des Plasmas durch den Schock und damit die Härte der Teilchenspektren überschätzen. In unseren zeit aufgelösten Berechnungen ist die maximale Kompression durch die limitierte verfügbare Zeit begrenzt. Zusätzlich zeigt sich das Auftreten einer Instabilität die durch die Rückkopplung der kosmischen Strahlung nahe der Kontaktdiskontinuität hervorgerufen wird.
KW - supernova remnant
KW - particle acceleration
KW - gamma rays
KW - Supernovaüberrest
KW - Teilchenbeschleunigung
KW - Gammastrahlung
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-470865
ER -
TY - JOUR
A1 - Garbe, Julius
A1 - Albrecht, Torsten
A1 - Levermann, Anders
A1 - Donges, Jonathan
A1 - Winkelmann, Ricarda
T1 - The hysteresis of the Antarctic Ice Sheet
JF - Nature : the international weekly journal of science
N2 - More than half of Earth's freshwater resources are held by the Antarctic Ice Sheet, which thus represents by far the largest potential source for global sea-level rise under future warming conditions(1). Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are lacking a comprehensive stability analysis of the Antarctic Ice Sheet for different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeodata(2)we find, using the Parallel Ice Sheet Model(3-5), that at global warming levels around 2 degrees Celsius above pre-industrial levels, West Antarctica is committed to long-term partial collapse owing to the marine ice-sheet instability. Between 6 and 9 degrees of warming above pre-industrial levels, the loss of more than 70 per cent of the present-day ice volume is triggered, mainly caused by the surface elevation feedback. At more than 10 degrees of warming above pre-industrial levels, Antarctica is committed to become virtually ice-free. The ice sheet's temperature sensitivity is 1.3 metres of sea-level equivalent per degree of warming up to 2 degrees above pre-industrial levels, almost doubling to 2.4 metres per degree of warming between 2 and 6 degrees and increasing to about 10 metres per degree of warming between 6 and 9 degrees. Each of these thresholds gives rise to hysteresis behaviour: that is, the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least one degree Celsius lower than pre-industrial levels. Our results show that if the Paris Agreement is not met, Antarctica's long-term sea-level contribution will dramatically increase and exceed that of all other sources.
Modelling shows that the Antarctic Ice Sheet exhibits multiple temperature thresholds beyond which ice loss would become irreversible, and once melted, the ice sheet can regain its previous mass only if the climate cools well below pre-industrial temperatures.
Y1 - 2020
U6 - https://doi.org/10.1038/s41586-020-2727-5
SN - 0028-0836
SN - 1476-4687
VL - 585
IS - 7826
SP - 538
EP - 544
PB - Macmillan Publishers Limited
CY - Berlin
ER -
TY - THES
A1 - Wang, Jingwen
T1 - Electret properties of polypropylene with surface chemical modification and crystalline reconstruction
N2 - As one of the most-produced commodity polymers, polypropylene draws considerable scientific and commercial interest as an electret material. In the present thesis, the influence of the surface chemical modification and crystalline reconstruction on the electret properties of the polypropylene thin films will be discussed. The chemical treatment with orthophosphoric acid can significantly improve the surface charge stability of the polypropylene electrets by introducing phosphorus- and oxygen-containing structures onto the modified surface. The thermally stimulated discharge measurement and charge profiling by means of piezoelectrically generated pressure steps are used to investigate the electret behaviour. It is concluded that deep traps of limited number density are created during the treatment with inorganic chemicals. Hence, the improvement dramatically decreases when the surface-charge density is substantially higher than ±1.2×10^(-3) C·m^(-2). The newly formed traps also show a higher trapping energy for negative charges. The energetic distributions of the traps in the non-treated and chemically treated samples offer an insight regarding the surface and foreign-chemical dominance on the charge storage and transport in the polypropylene electrets.
Additionally, different electret properties are observed on the polypropylene films with the spherulitic and transcrystalline structures. It indicates the dependence of the charge storage and transport on the crystallite and molecular orientations in the crystalline phase. In general, a more diverse crystalline growth in the spherulitic samples can result in a more complex energetic trap distribution, in comparison to that in a transcrystalline polypropylene. The double-layer transcrystalline polypropylene film with a crystalline interface in the middle can be obtained by crystallising the film in contact with rough moulding surfaces on both sides. A layer of heterocharges appears on each side of the interface in the double-layer transcrystalline polypropylene electrets after the thermal poling. However, there is no charge captured within the transcrystalline layers. The phenomenon reveals the importance of the crystalline interface in terms of creating traps with the higher activation energy in polypropylene. The present studies highlight the fact that even slight variations in the polypropylene film may lead to dramatic differences in its electret properties.
N2 - Als eines der meistproduzierten Polymere stößt Polypropylen (PP) auch als Elektretmaterial auf großes wissenschaftliches und kommerzielles Interesse. In der vorliegenden Arbeit wird der Einfluss chemischer Oberflächen-Modifikationen und kristalliner Rekonstruktionen auf die Elektreteigenschaften von dünnen Polypropylen-Schichten untersucht und diskutiert. Die nasschemische Behandlung mit Orthophosphorsäure kann die Oberflächenladungsstabilität der PP-Elektrete deutlich verbessern, indem phosphor- und sauerstoffhaltige Strukturen auf der modifizierten Oberfläche erzeugt und verankert werden. Aus thermisch stimulierten Entladungsexperimenten und Ladungsmessungen mit piezoelektrisch erzeugten Druckstufen ergibt sich, dass die Oberflächenbehandlung eine begrenzte Anzahl tiefer Haftstellen vor allem für negative Ladungen erzeugt. Daher nimmt die Verbesserung drastisch ab, wenn die Oberflächenladungsdichte einen wesentlich höheren Wert als ±1.2×10-3 C·m-2 hat. Die energetischen Verteilungen der Ladungsfallen in unbehandelten und in chemisch behandelten Proben ermöglichen Rückschlüsse auf die Oberfläche und auf die wesentliche Rolle der aufgebrachten chemischen Spezies für Ladungsspeicherung und -transport in PP-Elektreten.
Darüber hinaus werden an dünnen Polypropylenfolien mit entweder sphärolithischen oder transkristallinen Strukturen deutlich unterschiedliche Elektreteigenschaften beobachtet, was den starken Einfluss von Kristallstruktur und Molekülorientierung auf Ladungsspeicherung und -transport in der kristallinen Phase anzeigt. Generell führt das vielfältigere kristalline Wachstum in sphärolithischen Proben oft zu komplexeren energetischen Verteilungen der Ladungsfallen als in transkristallinen PP-Schichten. Zweischichtige transkristalline PP-Folien mit einer kristallinen Grenzfläche in der Mitte können durch beidseitige Kristallisation auf rauen Formgussoberflächen erzeugt werden. Auf jeder Seite der Grenzfläche in der Mitte der zweischichtigen transkristallinen PP-Elektrete findet sich nach thermischer Polung eine Schicht von Heteroladungen, während innerhalb der transkristallinen Schichten keine Ladungen beobachtet werden. Daraus wird die Bedeutung der kristallinen Grenzfläche für das Auftreten von Ladungsfallen mit hohen Aktivierungsenergien in Polypropylen deutlich. Die vorliegenden Studien zeigen, dass bereits geringe Variationen in der Nanostruktur der Polypropylenfolien zu dramatisch unterschiedlichen Elektreteigenschaften führen können.
KW - electret
KW - polypropylene
KW - charge storage and transport
KW - surface chemical treatment
KW - transcrystalline polypropylene
KW - Elektret
KW - Polypropylen
KW - Ladungsspeicherung und -transport
KW - chemische Oberflächen-Modifikationen
KW - transkristallines Polypropylen
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-470271
ER -
TY - JOUR
A1 - Phuong, Le Quang
A1 - Hosseini, Seyed Mehrdad
A1 - Sandberg, Oskar J.
A1 - Zou, Yingping
A1 - Woo, Han Young
A1 - Neher, Dieter
A1 - Shoaee, Safa
T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells
JF - Solar RRL
N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
KW - nonfullerene acceptors
KW - organic solar cells
KW - quasi-Fermi level
KW - splitting
KW - quasi-steady-state photoinduced absorptions
KW - surface
KW - recombinations
KW - voltage losses
Y1 - 2020
U6 - https://doi.org/10.1002/solr.202000649
SN - 2367-198X
VL - 5
IS - 1
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Tokmoldin, Nurlan
A1 - Hosseini, Seyed Mehrdad
A1 - Raoufi, Meysam
A1 - Phuong, Le Quang
A1 - Sandberg, Oskar J.
A1 - Guan, Huilan
A1 - Zou, Yingping
A1 - Neher, Dieter
A1 - Shoaee, Safa
T1 - Extraordinarily long diffusion length in PM6:Y6 organic solar cells
JF - Journal of materials chemistry : A, materials for energy and sustainability
N2 - The PM6:Y6 bulk-heterojunction (BHJ) blend system achieves high short-circuit current (J(SC)) values in thick photovoltaic junctions. Here we analyse these solar cells to understand the observed independence of the short-circuit current upon photoactive layer thickness. We employ a range of optoelectronic measurements and analyses, including Mott-Schottky analysis, CELIV, photoinduced absorption spectroscopy, mobility measurements and simulations, to conclude that, the invariant photocurrent for the devices with different active layer thicknesses is associated with the Y6's diffusion length exceeding 300 nm in case of a 300 nm thick cell. This is despite unintentional doping that occurs in PM6 and the associated space-charge effect, which is expected to be even more profound upon photogeneration. This extraordinarily long diffusion length - which is an order of magnitude larger than typical values for organics - dominates transport in the flat-band region of thick junctions. Our work suggests that the performance of the doped PM6:Y6 organic solar cells resembles that of inorganic devices with diffusion transport playing a pivotal role. Ultimately, this is expected to be a key requirement for the fabrication of efficient, high-photocurrent, thick organic solar cells.
Y1 - 2020
U6 - https://doi.org/10.1039/d0ta03016c
SN - 2050-7488
SN - 2050-7496
VL - 8
IS - 16
SP - 7854
EP - 7860
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Zu, Fengshuo
A1 - Schultz, Thorsten
A1 - Wolff, Christian Michael
A1 - Shin, Dongguen
A1 - Frohloff, Lennart
A1 - Neher, Dieter
A1 - Amsalem, Patrick
A1 - Koch, Norbert
T1 - Position-locking of volatile reaction products by atmosphere and capping layers slows down photodecomposition of methylammonium lead triiodide perovskite
JF - RSC Advances
N2 - The remarkable progress of metal halide perovskites in photovoltaics has led to the power conversion efficiency approaching 26%. However, practical applications of perovskite-based solar cells are challenged by the stability issues, of which the most critical one is photo-induced degradation. Bare CH3NH3PbI3 perovskite films are known to decompose rapidly, with methylammonium and iodine as volatile species and residual solid PbI2 and metallic Pb, under vacuum under white light illumination, on the timescale of minutes. We find, in agreement with previous work, that the degradation is non-uniform and proceeds predominantly from the surface, and that illumination under N-2 and ambient air (relative humidity 20%) does not induce substantial degradation even after several hours. Yet, in all cases the release of iodine from the perovskite surface is directly identified by X-ray photoelectron spectroscopy. This goes in hand with a loss of organic cations and the formation of metallic Pb. When CH3NH3PbI3 films are covered with a few nm thick organic capping layer, either charge selective or non-selective, the rapid photodecomposition process under ultrahigh vacuum is reduced by more than one order of magnitude, and becomes similar in timescale to that under N-2 or air. We conclude that the light-induced decomposition reaction of CH3NH3PbI3, leading to volatile methylammonium and iodine, is largely reversible as long as these products are restrained from leaving the surface. This is readily achieved by ambient atmospheric pressure, as well as a thin organic capping layer even under ultrahigh vacuum. In addition to explaining the impact of gas pressure on the stability of this perovskite, our results indicate that covalently "locking" the position of perovskite components at the surface or an interface should enhance the overall photostability.
Y1 - 2020
U6 - https://doi.org/10.1039/d0ra03572f
SN - 2046-2069
VL - 10
IS - 30
SP - 17534
EP - 17542
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Singh, Rishu Kumar
A1 - Metzler, Ralf
A1 - Sandev, Trifce
T1 - Resetting dynamics in a confining potential
JF - Journal of physics : A, Mathematical and theoretical
N2 - We study Brownian motion in a confining potential under a constant-rate resetting to a reset position x(0). The relaxation of this system to the steady-state exhibits a dynamic phase transition, and is achieved in a light cone region which grows linearly with time. When an absorbing boundary is introduced, effecting a symmetry breaking of the system, we find that resetting aids the barrier escape only when the particle starts on the same side as the barrier with respect to the origin. We find that the optimal resetting rate exhibits a continuous phase transition with critical exponent of unity. Exact expressions are derived for the mean escape time, the second moment, and the coefficient of variation (CV).
KW - diffusion
KW - resetting
KW - barrier escape
KW - first-passage
Y1 - 2020
U6 - https://doi.org/10.1088/1751-8121/abc83a
SN - 1751-8113
SN - 1751-8121
VL - 53
IS - 50
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - THES
A1 - Wolff, Christian Michael
T1 - Identification and reduction of losses in perovskite solar cells
N2 - Perovskite solar cells have become one of the most studied systems in the quest for new, cheap and efficient solar cell materials. Within a decade device efficiencies have risen to >25% in single-junction and >29% in tandem devices on top of silicon. This rapid improvement was in many ways fortunate, as e. g. the energy levels of commonly used halide perovskites are compatible with already existing materials from other photovoltaic technologies such as dye-sensitized or organic solar cells. Despite this rapid success, fundamental working principles must be understood to allow concerted further improvements. This thesis focuses on a comprehensive understanding of recombination processes in functioning devices.
First the impact the energy level alignment between the perovskite and the electron transport layer based on fullerenes is investigated. This controversial topic is comprehensively addressed and recombination is mitigated through reducing the energy difference between the perovskite conduction band minimum and the LUMO of the fullerene. Additionally, an insulating blocking layer is introduced, which is even more effective in reducing this recombination, without compromising carrier collection and thus efficiency. With the rapid efficiency development (certified efficiencies have broken through the 20% ceiling) and thousands of researchers working on perovskite-based optoelectronic devices, reliable protocols on how to reach these efficiencies are lacking. Having established robust methods for >20% devices, while keeping track of possible pitfalls, a detailed description of the fabrication of perovskite solar cells at the highest efficiency level (>20%) is provided. The fabrication of low-temperature p-i-n structured devices is described, commenting on important factors such as practical experience, processing atmosphere & temperature, material purity and solution age. Analogous to reliable fabrication methods, a method to identify recombination losses is needed to further improve efficiencies. Thus, absolute photoluminescence is identified as a direct way to quantify the Quasi-Fermi level splitting of the perovskite absorber (1.21eV) and interfacial recombination losses the transport layers impose, reducing the latter to ~1.1eV. Implementing very thin interlayers at both the p- and n-interface (PFN-P2 and LiF, respectively), these losses are suppressed, enabling a VOC of up to 1.17eV. Optimizing the device dimensions and the bandgap, 20% devices with 1cm2 active area are demonstrated. Another important consideration is the solar cells’ stability if subjected to field-relevant stressors during operation. In particular these are heat, light, bias or a combination thereof. Perovskite layers – especially those incorporating organic cations – have been shown to degrade if subjected to these stressors. Keeping in mind that several interlayers have been successfully used to mitigate recombination losses, a family of perfluorinated self-assembled monolayers (X-PFCn, where X denotes I/Br and n = 7-12) are introduced as interlayers at the n-interface. Indeed, they reduce interfacial recombination losses enabling device efficiencies up to 21.3%. Even more importantly they improve the stability of the devices. The solar cells with IPFC10 are stable over 3000h stored in the ambient and withstand a harsh 250h of MPP at 85◦C without appreciable efficiency losses. To advance further and improve device efficiencies, a sound understanding of the photophysics of a device is imperative. Many experimental observations in recent years have however drawn an inconclusive picture, often suffering from technical of physical impediments, disguising e. g. capacitive discharge as recombination dynamics. To circumvent these obstacles, fully operational, highly efficient perovskites solar cells are investigated by a combination of multiple optical and optoelectronic probes, allowing to draw a conclusive picture of the recombination dynamics in operation. Supported by drift-diffusion simulations, the device recombination dynamics can be fully described by a combination of first-, second- and third-order recombination and JV curves as well as luminescence efficiencies over multiple illumination intensities are well described within the model. On this basis steady state carrier densities, effective recombination constants, densities-of-states and effective masses are calculated, putting the devices at the brink of the radiative regime. Moreover, a comprehensive review of recombination in state-of-the-art devices is given, highlighting the importance of interfaces in nonradiative recombination. Different strategies to assess these are discussed, before emphasizing successful strategies to reduce interfacial recombination and pointing towards the necessary steps to further improve device efficiency and stability. Overall, the main findings represent an advancement in understanding loss mechanisms in highly efficient solar cells. Different reliable optoelectronic techniques are used and interfacial losses are found to be of grave importance for both efficiency and stability. Addressing the interfaces, several interlayers are introduced, which mitigate recombination losses and degradation.
N2 - Auf der Suche nach neuen, kostengünstigen und effizienten Systemen zur photovoltaischen Energiegewinnung, sind Perowskit Solarzellen zu einem der am meistuntersuchtesten Systeme avanciert. Innerhalb einer Dekade konnten unabhängig zertifizierte Umwandlungseffizienzen von >25% in Einzelschicht- und >29% in Mehrschichtzellen basierend auf Siliziumzellen realisiert werden. Die schnelle Entwicklung war in vielerlei Hinsicht glücklich, da beispielsweise die Energielevel typischer Perowskitschichten mit bereits existierenden Kontaktschichtsystemen anderer Photovoltaiksysteme, wie etwa Farbstoffsolarzellen oder Organische Solarzellen, kompatibel sind. Trotz dieses schnellen Erfolges, müssen zur weiteren Effizienzsteigerung grundlegende Wirkprinzipien der Solarzellen verstanden werden. Diese Arbeit beschäftigt sich mit dem umfassenden Verständnis von Rekombinationsprozessen in voll funktionstüchtigen Bauteilen. Zunächst wird der Einfluss unterschiedlicher Energielevel einer Transportschicht, basierend auf Fullerenen untersucht. Dieses kontrovers diskutierte Thema wurde umfassend untersucht und Rekombinationsverluste aufgrund ungünstiger Energielevel reduziert indem - durch die Wahl unterschiedlicher Fulleren-Derivate - der energetische Abstand zwischen Leitungsband des Perowskit und dem niedrigsten unbesetzten Zustand des Fullerenes reduziert wird. Zusätzlich wurde eine ultradünne elektrisch isolierende Zwischenschicht eingebracht, die noch effektiver Rekombinationsverluste unterdrückt, ohne die Fähigkeit zur Ladungsextraktion - und damit Effizienz einzuschränken. Das breite Interesse tausender Forschenden weltweit hat zur schnellen Entwicklung besagter hoher Effizienzen geführt, obgleich verlässliche, leicht nachzuvollziehende Herstellungsprotokolle nicht existierten. Auf Basis der hier entwickelten Protokolle, werden Methoden dargestellt, mit denen verlässlich >20% effiziente Solarzellen produziert werden können. Hierbei wird insbesondere auf sogenannte invertierte (p-i-n) Zellen eingegangen, wobei ein Fokus auf der Beschreibung essentieller Faktoren wie Atmosphärenkontrolle, Temperaturkontrolle, Materialreinheit oder praktischer Erfahrung liegt. Analog zu verlässlichen Herstellungsmethoden bedarf es robuster Techniken um Rekombinationsverluste zu identifizieren und zu lokalisieren. Zu diesem Zweck wird die Messung der absoluten Photolumineszenzeffizienz eingeführt, die erlaubt die Aufspaltung der Quasi-Fermi Level des Perowskiten zu quantifizieren (1.22eV). Ebenso ist es mit dieser Methode möglich Rekombinationsverluste an Grenzflächen zu lokalisieren, die die Leerlaufspannung auf 1.1V limitieren. Zur Vermeidung dieser Verluste werden erneut ultradünne Zwischenschichten an sowohl der p- als auch n- Grenzschicht eingebracht (PFN-P2 und LiF), die Leerlaufspannungen von bis zu 1.17V ermöglichen. Mithilfe eines optimierten Designs und einer Reduzierung der Bandlücke können Bauteile mit 20% Effizienz bei einer Größe von 1cm2 realisiert werden. Nebst hoher Effizienz ist die Stabilität der Bauteile unter einsatzrelevanten Umweltbedingungen ein wichtiger Faktor auf dem Weg zu einer Kommerzialisierung. Dies gilt insbesondere für Hitze, Beleuchtung, elektrische Ladung oder eine Kombination letzterer. Perowskitschichten -- insbesondere diejenigen, die organische Kationen beinhalten -- sind wohlbekannt dafür unter genannten Bedingungen zu degradieren. Das Konzept der ultradünnen Zwischenschichten wird daher um eine Familie fluornierter selbstorganisierender molekularer Monoschichten erweitert X-PFC_n, wobei X ein Halogen I/Br darstellt und n = 7-12 die Länge der fluorinerten Alkylkette angibt), die an der n-Grenzfläche zum Einsatz kommen. Diese Zwischenschicht reduziert Rekombinationsverluste resultierend in 21.3% effizienten Bauteilen und ermöglicht zusätzlich eine drastische erhöhte Stabilität. Bauteile mit dem Molekül IPFC10 sind über 3000h stabil unter Lagerungsbedingungen im Dunkeln und überstehen 250h unter voller Last bei 85°C ohne nennenswerte Verluste. Weitere Fortschritte in der Steigerung der Effizienz sind nur zu erwarten, wenn eine vollständige Beschreibung der Wirkprinzipien und Schwachstellen vorliegt. Eine Vielzahl experimenteller Studien haben bisher jedoch ein lückenhaftes Bild gemalt. Häufig sind physikalische Beschränkungen, etwa die hohe Kapazität aufgrund der sehr dünnen Schichten dafür verantwortlich, dass Rekombinationsdynamiken durch kapazitive Entladungsprozesse verdeckt werden. Um diese Probleme zu umgehen, werden hocheffiziente Solarzellen mit einer Kombination mehrerer optischer und optoelektronischer Messmethoden untersucht. Dies ermöglicht die Rekombinationsdynamik mit einer Superposition aus Rekombination erster, zweiter und dritter Ordnung der Ladungsträgerdichte vollumfänglich zu beschreiben. Drift-Diffusions Simulationen unterstützen die experimentellen Ergebnisse, selbst unter Einbeziehung mobiler Ionen. Weiterhin wird in einem Übersichtsartikel ein Ausblick auf den gegenwärtigen Stand des Wissens im Bezug auf Rekombinationsverluste in besagten Solarzellen gegeben. Unterschiedliche Messmethoden werden vorgestellt und erfolgreiche Methoden zur Minderung genannter Verluste diskutiert. Insgesamt stellt diese Arbeit einen Fortschritt im Verständnis und der Verminderung unterschiedlicher Verlustprozesse dar. Mithilfe unterschiedlicher verlässlicher optoelektronischer Messmethoden, wird gezeigt, dass der Ursprung von Rekombinations- und Stabilitätsverlusten häufig an den Grenzflächen liegt. Mithilfe gezielt eingesetzter ultradünner Zwischenschichten werden diese Verluste reduziert und die Stabilität erhöht.
T2 - Identifizierung und Reduzierung von Verlusten in Perowskit Solarzellen
KW - perovskite solar cells
KW - interfacial recombination
KW - nonradiative losses
KW - Perowskit Solarzellen
KW - Grenzflächenrekombination
KW - nichtstrahlende Verluste
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-479301
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 - GEN
A1 - Phuong, Le Quang
A1 - Hosseini, Seyed Mehrdad
A1 - Sandberg, Oskar J.
A1 - Zou, Yingping
A1 - Woo, Han Young
A1 - Neher, Dieter
A1 - Shoaee, Safa
T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells
T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1384
KW - nonfullerene acceptors
KW - organic solar cells
KW - quasi-Fermi level
KW - splitting
KW - quasi-steady-state photoinduced absorptions
KW - surface
KW - recombinations
KW - voltage losses
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-570018
SN - 1866-8372
IS - 1
ER -
TY - JOUR
A1 - Wunderling, Nico
A1 - Willeit, Matteo
A1 - Donges, Jonathan
A1 - Winkelmann, Ricarda
T1 - Global warming due to loss of large ice masses and Arctic summer sea ice
JF - Nature Communications
N2 - Several large-scale cryosphere elements such as the Arctic summer sea ice, the mountain glaciers, the Greenland and West Antarctic Ice Sheet have changed substantially during the last century due to anthropogenic global warming. However, the impacts of their possible future disintegration on global mean temperature (GMT) and climate feedbacks have not yet been comprehensively evaluated. Here, we quantify this response using an Earth system model of intermediate complexity. Overall, we find a median additional global warming of 0.43 degrees C (interquartile range: 0.39-0.46 degrees C) at a CO2 concentration of 400 ppm. Most of this response (55%) is caused by albedo changes, but lapse rate together with water vapour (30%) and cloud feedbacks (15%) also contribute significantly. While a decay of the ice sheets would occur on centennial to millennial time scales, the Arctic might become ice-free during summer within the 21st century. Our findings imply an additional increase of the GMT on intermediate to long time scales. The disintegration of cryosphere elements such as the Arctic summer sea ice, mountain glaciers, Greenland and West Antarctica is associated with temperature and radiative feedbacks. In this work, the authors quantify these feedbacks and find an additional global warming of 0.43 degrees C.
Y1 - 2020
U6 - https://doi.org/10.1038/s41467-020-18934-3
SN - 2041-1723
VL - 11
IS - 1
PB - Nature Publishing Group
CY - Berlin
ER -
TY - JOUR
A1 - Hosseini, Seyed Mehrdad
A1 - Tokmoldin, Nurlan
A1 - Lee, Young Woong
A1 - Zou, Yingping
A1 - Woo, Han Young
A1 - Neher, Dieter
A1 - Shoaee, Safa
T1 - Putting order into PM6:Y6 solar cells to reduce the langevin recombination in 400 nm thick junction
JF - Solar RRL
N2 - Increasing the active layer thickness without sacrificing the power conversion efficiency (PCE) is one of the great challenges faced by organic solar cells (OSCs) for commercialization. Recently, PM6:Y6 as an OSC based on a non-fullerene acceptor (NFA) has excited the community because of its PCE reaching as high as 15.9%; however, by increasing the thickness, the PCE drops due to the reduction of the fill factor (FF). This drop is attributed to change in mobility ratio with increasing thickness. Furthermore, this work demonstrates that by regulating the packing and the crystallinity of the donor and the acceptor, through volumetric content of chloronaphthalene (CN) as a solvent additive, one can improve the FF of a thick PM6:Y6 device (approximate to 400 nm) from 58% to 68% (PCE enhances from 12.2% to 14.4%). The data indicate that the origin of this enhancement is the reduction of the structural and energetic disorders in the thick device with 1.5% CN compared with 0.5% CN. This correlates with improved electron and hole mobilities and a 50% suppressed bimolecular recombination, such that the non-Langevin reduction factor is 180 times. This work reveals the role of disorder on the charge extraction and bimolecular recombination of NFA-based OSCs.
KW - charge carrier extraction
KW - energetic disorders
KW - non-fullerene acceptors
KW - non-Langevin reduction factors
KW - thick junctions
Y1 - 2020
U6 - https://doi.org/10.1002/solr.202000498
SN - 2367-198X
VL - 4
IS - 11
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - García-Benito, Inés
A1 - Quarti, Claudio
A1 - Queloz, Valentin I. E.
A1 - Hofstetter, Yvonne J.
A1 - Becker-Koch, David
A1 - Caprioglio, Pietro
A1 - Neher, Dieter
A1 - Orlandi, Simonetta
A1 - Cavazzini, Marco
A1 - Pozzi, Gianluca
A1 - Even, Jacky
A1 - Nazeeruddin, Mohammad Khaja
A1 - Vaynzof, Yana
A1 - Grancini, Giulia
T1 - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
JF - Frontiers in Chemistry
N2 - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
KW - fluorinated organic spacer
KW - 2D perovskites
KW - phase transition
KW - temperature dependence
KW - excitonic materials
Y1 - 2020
U6 - https://doi.org/10.3389/fchem.2019.00946
SN - 2296-2646
VL - 7
SP - 1
EP - 11
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Varykhalov, Andrei
A1 - Freyse, Friedrich
A1 - Aguilera, Irene
A1 - Battiato, Marco
A1 - Krivenkov, Maxim
A1 - Marchenko, Dmitry
A1 - Bihlmayer, Gustav
A1 - Blugel, Stefan
A1 - Rader, Oliver
A1 - Sanchez-Barriga, Jaime
T1 - Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well
JF - Physical Review Research
N2 - We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics.
KW - AG
KW - Flims
Y1 - 2020
U6 - https://doi.org/10.1103/PhysRevResearch.2.013343
SN - 0031-9007
VL - 2
IS - 1
SP - 1
EP - 9
PB - American Physical Society
CY - Ridge, NY
ER -
TY - JOUR
A1 - Mansour, Ahmed E.
A1 - Lungwitz, Dominique
A1 - Schultz, Thorsten
A1 - Arvind, Malavika
A1 - Valencia, Ana M.
A1 - Cocchi, Caterina
A1 - Opitz, Andreas
A1 - Neher, Dieter
A1 - Koch, Norbert
T1 - The optical signatures of molecular-doping induced polarons in poly(3-hexylthiophene-2,5-diyl)
BT - individual polymer chains versus aggregates
JF - Journal of materials chemistry : C, Materials for optical and electronic devices
N2 - Optical absorption spectroscopy is a key method to investigate doped conjugated polymers and to characterize the doping-induced charge carriers, i.e., polarons. For prototypical poly(3-hexylthiophene-2,5-diyl) (P3HT), the absorption intensity of molecular dopant induced polarons is widely used to estimate the carrier density and the doping efficiency, i.e., the number of polarons formed per dopant molecule. However, the dependence of the polaron-related absorption features on the structure of doped P3HT, being either aggregates or separated individual chains, is not comprehensively understood in contrast to the optical absorption features of neutral P3HT. In this work, we unambiguously differentiate the optical signatures of polarons on individual P3HT chains and aggregates in solution, notably the latter exhibiting the same shape as aggregates in solid thin films. This is enabled by employing tris(pentafluorophenyl)borane (BCF) as dopant, as this dopant forms only ion pairs with P3HT and no charge transfer complexes, and BCF and its anion have no absorption in the spectral region of P3HT polarons. Polarons on individual chains exhibit absorption peaks at 1.5 eV and 0.6 eV, whereas in aggregates the high-energy peak is split into a doublet 1.3 eV and 1.65 eV, and the low-energy peak is shifted below 0.5 eV. The dependence of the fraction of solvated individual chains versus aggregates on absolute solution concentration, dopant concentration, and temperature is elucidated, and we find that aggregates predominate in solution under commonly used processing conditions. Aggregates in BCF-doped P3HT solution can be effectively removed upon simple filtering. From varying the filter pore size (down to 200 nm) and thin film morphology characterization with scanning force microscopy we reveal the aggregates' size dependence on solution absolute concentration and dopant concentration. Furthermore, X-ray photoelectron spectroscopy shows that the dopant loading in aggregates is higher than for individual P3HT chains. The results of this study help understanding the impact of solution pre-aggregation on thin film properties of molecularly doped P3HT, and highlight the importance of considering such aggregation for other doped conjugated polymers in general.
Y1 - 2020
U6 - https://doi.org/10.1039/c9tc06509a
SN - 2050-7526
SN - 2050-7534
VL - 8
IS - 8
SP - 2870
EP - 2879
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Poudel, Amit
A1 - Tichy, Wolfgang
A1 - Brügmann, Bernd
A1 - Dietrich, Tim
T1 - Increasing the accuracy of binary neutron star simulations with an improved vacuum treatment
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - Numerical-relativity simulations are essential for studying the last stages of the binary neutron star coalescence. Unfortunately, for stable simulations there is the need to add an artificial low-density atmosphere. Here we discuss a new framework in which we can effectively set the density surrounding the neutron stars to zero to ensure a more accurate simulation. We test our method with a number of single star test cases and for an equal-mass binary neutron star simulation. While the bulk motion of the system is not influenced, and hence there is no improvement with respect to the emitted gravitational-wave signal, we find that the new approach is superior with respect to mass conservation and it allows a much better tracking of outward moving material. This will allow a more accurate simulation of the ejected material and supports the interpretation of present and future multimessenger observations with more accurate numerical-relativity simulations.
Y1 - 2020
U6 - https://doi.org/10.1103/PhysRevD.102.104014
SN - 2470-0010
SN - 2470-0029
VL - 102
IS - 10
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Samajdar, Anuradha
A1 - Dietrich, Tim
T1 - Constructing Love-Q relations with gravitational wave detections
JF - Physical review : D, Particles, fields, gravitation, and cosmology
N2 - Quasiuniversal relations between the tidal deformability and the quadrupole moment of neutron stars are predicted by theoretical computations, but have not been measured experimentally. We simulate 120 binary neutron star sources and find that Advanced LIGO and Advanced Virgo at design sensitivity could find possible deviations from predicted relations if the neutron stars are highly spinning. A network of envisaged third generation detectors will even allow extracting such relations, providing new tests of general relativity and nuclear physics predictions.
Y1 - 2020
U6 - https://doi.org/10.1103/PhysRevD.101.124014
SN - 1550-7998
SN - 1550-2368
VL - 101
IS - 12
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Mejia-Monasterio, Carlos
A1 - Metzler, Ralf
A1 - Vollmer, Jürgen
T1 - Editorial: anomalous transport
BT - applications, mathematical perspectives, and big data
JF - Frontiers in Physics
KW - anomalous (or non-Fickian) diffusion
KW - anomalous heat conduction
KW - stochastic dynamics
KW - molecular overcrowding
KW - dynamical systems
Y1 - 2020
U6 - https://doi.org/10.3389/fphy.2020.622417
SN - 2296-424X
VL - 8
PB - Frontiers Media
CY - Lausanne
ER -
TY - GEN
A1 - García-Benito, Inés
A1 - Quarti, Claudio
A1 - Queloz, Valentin I. E.
A1 - Hofstetter, Yvonne J.
A1 - Becker-Koch, David
A1 - Caprioglio, Pietro
A1 - Neher, Dieter
A1 - Orlandi, Simonetta
A1 - Cavazzini, Marco
A1 - Pozzi, Gianluca
A1 - Even, Jacky
A1 - Nazeeruddin, Mohammad Khaja
A1 - Vaynzof, Yana
A1 - Grancini, Giulia
T1 - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1421
KW - fluorinated organic spacer
KW - 2D perovskites
KW - phase transition
KW - temperature dependence
KW - excitonic materials
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-512420
SN - 1866-8372
ER -
TY - JOUR
A1 - Smirnov, Artem
A1 - Berrendorf, Max
A1 - Shprits, Yuri Y.
A1 - Kronberg, Elena A.
A1 - Allison, Hayley J.
A1 - Aseev, Nikita
A1 - Zhelavskaya, Irina
A1 - Morley, Steven K.
A1 - Reeves, Geoffrey D.
A1 - Carver, Matthew R.
A1 - Effenberger, Frederic
T1 - Medium energy electron flux in earth's outer radiation
belt (MERLIN)
BT - a Machine learning model
JF - Space weather : the international journal of research and applications
N2 - The radiation belts of the Earth, filled with energetic electrons, comprise complex and dynamic systems that pose a significant threat to satellite operation. While various models of electron flux both for low and relativistic energies have been developed, the behavior of medium energy (120-600 keV) electrons, especially in the MEO region, remains poorly quantified. At these energies, electrons are driven by both convective and diffusive transport, and their prediction usually requires sophisticated 4D modeling codes. In this paper, we present an alternative approach using the Light Gradient Boosting (LightGBM) machine learning algorithm. The Medium Energy electRon fLux In Earth's outer radiatioN belt (MERLIN) model takes as input the satellite position, a combination of geomagnetic indices and solar wind parameters including the time history of velocity, and does not use persistence. MERLIN is trained on >15 years of the GPS electron flux data and tested on more than 1.5 years of measurements. Tenfold cross validation yields that the model predicts the MEO radiation environment well, both in terms of dynamics and amplitudes o f flux. Evaluation on the test set shows high correlation between the predicted and observed electron flux (0.8) and low values of absolute error. The MERLIN model can have wide space weather applications, providing information for the scientific community in the form of radiation belts reconstructions, as well as industry for satellite mission design, nowcast of the MEO environment, and surface charging analysis.
KW - machine learning
KW - radiation belts
KW - electron flux
KW - empirical modeling
KW - magnetosphere
KW - electrons
Y1 - 2020
U6 - https://doi.org/10.1029/2020SW002532
SN - 1542-7390
VL - 18
IS - 11
PB - American geophysical union, AGU
CY - Washington
ER -
TY - JOUR
A1 - Erler, Alexander
A1 - Riebe, Daniel
A1 - Beitz, Toralf
A1 - Löhmannsröben, Hans-Gerd
A1 - Grothusheitkamp, Daniela
A1 - Kunz, Thomas
A1 - Methner, Frank-Jürgen
T1 - Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry
JF - Journal of mass spectrometr
N2 - The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on-site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)-mass spectrometry (MS). The APCI source utilizes soft X-radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on-site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI-MS. Accordingly, more than 90% of the volatile metabolites found by APCI-MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC-IMS.
KW - APCI
KW - fungus
KW - gas chromatography
KW - ion mobility spectrometry
KW - mass
KW - spectrometry
KW - mold
KW - soft X-ray
Y1 - 2020
U6 - https://doi.org/10.1002/jms.4501
SN - 1076-5174
SN - 1096-9888
VL - 55
IS - 5
SP - 1
EP - 10
PB - Wiley
CY - Hoboken
ER -
TY - JOUR
A1 - Chen, Junchao
A1 - Lange, Thomas
A1 - Andjelkovic, Milos
A1 - Simevski, Aleksandar
A1 - Krstić, Miloš
T1 - Prediction of solar particle events with SRAM-based soft error rate monitor and supervised machine learning
JF - Microelectronics reliability
N2 - This work introduces an embedded approach for the prediction of Solar Particle Events (SPEs) in space applications by combining the real-time Soft Error Rate (SER) measurement with SRAM-based detector and the offline trained machine learning model. The proposed approach is intended for the self-adaptive fault-tolerant multiprocessing systems employed in space applications. With respect to the state-of-the-art, our solution allows for predicting the SER 1 h in advance and fine-grained hourly tracking of SER variations during SPEs as well as under normal conditions. Therefore, the target system can activate the appropriate mechanisms for radiation hardening before the onset of high radiation levels. Based on the comparison of five different machine learning algorithms trained with the public space flux database, the preliminary results indicate that the best prediction accuracy is achieved with the recurrent neural network (RNN) with long short-term memory (LSTM).
Y1 - 2020
U6 - https://doi.org/10.1016/j.microrel.2020.113799
SN - 0026-2714
VL - 114
PB - Elsevier
CY - Oxford
ER -
TY - THES
A1 - Aseev, Nikita
T1 - Modeling and understanding dynamics of charged particles in the Earth's inner magnetosphere
T1 - Modellierung und Untersuchung der Dynamik geladener Teilchen in der inneren Magnetosphäre der Erde
N2 - The Earth's inner magnetosphere is a very dynamic system, mostly driven by the external solar wind forcing exerted upon the magnetic field of our planet. Disturbances in the solar wind, such as coronal mass ejections and co-rotating interaction regions, cause geomagnetic storms, which lead to prominent changes in charged particle populations of the inner magnetosphere - the plasmasphere, ring current, and radiation belts. Satellites operating in the regions of elevated energetic and relativistic electron fluxes can be damaged by deep dielectric or surface charging during severe space weather events. Predicting the dynamics of the charged particles and mitigating their effects on the infrastructure is of particular importance, due to our increasing reliance on space technologies.
The dynamics of particles in the plasmasphere, ring current, and radiation belts are strongly coupled by means of collisions and collisionless interactions with electromagnetic fields induced by the motion of charged particles. Multidimensional numerical models simplify the treatment of transport, acceleration, and loss processes of these particles, and allow us to predict how the near-Earth space environment responds to solar storms. The models inevitably rely on a number of simplifications and assumptions that affect model accuracy and complicate the interpretation of the results. In this dissertation, we quantify the processes that control electron dynamics in the inner magnetosphere, paying particular attention to the uncertainties of the employed numerical codes and tools.
We use a set of convenient analytical solutions for advection and diffusion equations to test the accuracy and stability of the four-dimensional Versatile Electron Radiation Belt (VERB-4D) code. We show that numerical schemes implemented in the code converge to the analytical solutions and that the VERB-4D code demonstrates stable behavior independent of the assumed time step. The order of the numerical scheme for the convection equation is demonstrated to affect results of ring current and radiation belt simulations, and it is crucially important to use high-order numerical schemes to decrease numerical errors in the model.
Using the thoroughly tested VERB-4D code, we model the dynamics of the ring current electrons during the 17 March 2013 storm. The discrepancies between the model and observations above 4.5 Earth's radii can be explained by uncertainties in the outer boundary conditions. Simulation results indicate that the electrons were transported from the geostationary orbit towards the Earth by the global-scale electric and magnetic fields.
We investigate how simulation results depend on the input models and parameters. The model is shown to be particularly sensitive to the global electric field and electron lifetimes below 4.5 Earth's radii. The effects of radial diffusion and subauroral polarization streams are also quantified.
We developed a data-assimilative code that blends together a convection model of energetic electron transport and loss and Van Allen Probes satellite data by means of the Kalman filter. We show that the Kalman filter can correct model uncertainties in the convection electric field, electron lifetimes, and boundary conditions. It is also demonstrated how the innovation vector - the difference between observations and model prediction - can be used to identify physical processes missing in the model of energetic electron dynamics.
We computed radial profiles of phase space density of ultrarelativistic electrons, using Van Allen Probes measurements. We analyze the shape of the profiles during geomagnetically quiet and disturbed times and show that the formation of new local minimums in the radial profiles coincides with the ground observations of electromagnetic ion-cyclotron (EMIC) waves. This correlation indicates that EMIC waves are responsible for the loss of ultrarelativistic electrons from the heart of the outer radiation belt into the Earth's atmosphere.
N2 - Die innere Magnetosphäre der Erde ist ein sehr dynamisches System, das hauptsächlich vom äußeren Sonnenwind beeinflusst wird, der auf das Magnetfeld unseres Planeten einwirkt. Störungen im Sonnenwind, wie z.B. koronale Massenauswürfe und sogenannte Korotierende Wechselwirkungsbereiche, verursachen geomagnetische Stürme, die zu deutlichen Veränderungen der Populationen geladener Teilchen in der inneren Magnetosphäre führen - Plasmasphäre, Ringstrom und Strahlungsgürtel. Satelliten, die in Regionen mit erhöhten energetischen und relativistischen Elektronenflüssen betrieben werden, können durch tiefe dielektrische Ladung oder Oberflächenladungen bei schweren Weltraumwetterereignissen beschädigt werden. Die Vorhersage der Dynamik der geladenen Teilchen und die Abschwächung ihrer Auswirkungen auf die Infrastruktur sind heutzutage von besonderer Bedeutung, insbesondere aufgrund unserer zunehmenden Abhängigkeit von Weltraumtechnologien.
Die Dynamik von Teilchen in der Plasmasphäre, des Ringstrom und in den Strahlungsgürteln sind durch Kollisionen und kollisionsfreie Wechselwirkungen mit elektromagnetischen Feldern, die durch die Bewegung geladener Teilchen induziert werden, stark gekoppelt. Mehrdimensionale numerische Modelle vereinfachen die Betrachtung von Transport-, Beschleunigungs- und Verlustprozessen dieser Partikel und ermöglichen es uns, vorherzusagen, wie die erdnahe Weltraumumgebung auf Sonnenstürme reagiert. Die Modelle beruhen zwangsläufig auf einer Reihe von Vereinfachungen und Voraussetzungen, die sich auf die Modellgenauigkeit auswirken und die Interpretation der Ergebnisse erschweren. In dieser Dissertation quantifizieren wir die Prozesse, die die Dynamik der Elektronen in der inneren Magnetosphäre steuern. Dabei richten wir den Fokus insbesondere auch auf die Unsicherheiten der verwendeten numerischen Codes.
Wir verwenden eine Reihe praktischer analytischer Lösungen für Advektions- und Diffusionsgleichungen, um die Genauigkeit und Stabilität des 4-dimensionalen ''Versatile Electron Radiation Belt'' Codes (VERB-4D Code) zu testen. Wir zeigen, dass die im Code implementierten numerischen Schemata zu den analytischen Lösungen konvergieren und der Code sich unabhängig vom angenommenen Zeitschritt stabil verhält. Wir demonstrieren, wie die Genauigkeit des numerischen Schemas für die Konvektionsgleichung die Ergebnisse von Ringstrom- und Strahlungsgürtelsimulationen beeinflussen kann, und dass es von entscheidender Beteutung ist, numerische Schemata höherer Ordnung zu verwenden, um numerische Fehler im Modell zu reduzieren.
Mit dem ausführlich getesteten VERB-4D Code modellieren wir die Dynamik der Ringstromelektronen während des Sturms vom 17. März 2013. Wir zeigen, dass die Diskrepanzen zwischen dem Modell und Beobachtungen oberhalb von 4.5 Erdradien durch Unsicherheiten in den äußeren Randbedingungen erklärt werden können und dass die Elektronen durch die globalen elektrischen und magnetischen Felder von der geostationäre Umlaufbahn zur Erde transportiert wurden.
Wir untersuchen weiterhin, wie die Simulationsergebnisse von den Eingabemodellen und Parametern abhängen. Wir zeigen, dass das Modell besonders empfindlich für das globale elektrische Feld und die Lebensdauer der Elektronen unterhalb von 4.5 Erdradien ist. Außerdem quantifizieren wir auch die Auswirkungen von radialer Diffusion und subauroralen Polarisationsströmen.
Wir haben einen datenassimilativen Code entwickelt, der mithilfe des Kalman-Filters ein Konvektionsmodell für den Transport und den Verlust energetischer Elektronen mit den Satellitendaten der Van Allen Probes kombiniert. Wir zeigen, dass die Verwendung eines Kalman-Filters Modellunsicherheiten im elektrischen Konvektionsfeld, in der Lebensdauer der Elektronen und in den Randbedingungen korrigieren kann. Weiterhin zeigen wir, wie der Innovationsvektor - die Differenz zwischen Beobachtungen und Modellvorhersagen - verwendet werden kann, um physikalische Prozesse zu identifizieren, die im Modell der Dynamik der energetischen Elektronen fehlen.
Außerdem berechnen wir radiale Profile der Phasenraumdichte ultrarelativistischer Elektronen mithilfe von Van Allen Probes-Messungen. Wir analysieren die Form der Profile und zeigen, dass die Entstehung neuer lokaler Minima in den radialen Profilen mit den Bodenbeobachtungen von EMIC-Wellen übereinstimmt. Diese Korrelation legt nahe, dass EMIC-Wellen für den Verlust ultrarelativistischer Elektronen vom Herzen des äußeren Strahlungsgürtels in die Erdatmosphäre verantwortlich sind.
KW - ring current electrons
KW - radiation belts
KW - mathematical modeling
KW - wave-particle interactions
KW - data assimilation
KW - Ringstromelektronen
KW - Strahlungsgürtel
KW - mathematische Modellierung
KW - Wellen-Teilchen Wechselwirkungen
KW - Datenassimilation
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-479211
ER -
TY - JOUR
A1 - Perdigón-Toro, Lorena
A1 - Zhang, Huotian
A1 - Markina, Anastaa si
A1 - Yuan, Jun
A1 - Hosseini, Seyed Mehrdad
A1 - Wolff, Christian Michael
A1 - Zuo, Guangzheng
A1 - Stolterfoht, Martin
A1 - Zou, Yingping
A1 - Gao, Feng
A1 - Andrienko, Denis
A1 - Shoaee, Safa
A1 - Neher, Dieter
T1 - Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell
JF - Advanced materials
N2 - Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near-unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.
KW - driving force
KW - non-fullerene acceptors
KW - organic solar cells
KW - photocurrent generation
Y1 - 2020
U6 - https://doi.org/10.1002/adma.201906763
SN - 0935-9648
SN - 1521-4095
VL - 32
IS - 9
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Sandberg, Oskar J.
A1 - Kurpiers, Jona
A1 - Stolterfoht, Martin
A1 - Neher, Dieter
A1 - Meredith, Paul
A1 - Shoaee, Safa
A1 - Armin, Ardalan
T1 - On the question of the need for a built-in potential in Perovskite solar cells
JF - Advanced materials interfaces
N2 - Perovskite semiconductors as the active materials in efficient solar cells exhibit free carrier diffusion lengths on the order of microns at low illumination fluxes and many hundreds of nanometers under 1 sun conditions. These lengthscales are significantly larger than typical junction thicknesses, and thus the carrier transport and charge collection should be expected to be diffusion controlled. A consensus along these lines is emerging in the field. However, the question as to whether the built-in potential plays any role is still of matter of some conjecture. This important question using phase-sensitive photocurrent measurements and theoretical device simulations based upon the drift-diffusion framework is addressed. In particular, the role of the built-in electric field and charge-selective transport layers in state-of-the-art p-i-n perovskite solar cells comparing experimental findings and simulation predictions is probed. It is found that while charge collection in the junction does not require a drift field per se, a built-in potential is still needed to avoid the formation of reverse electric fields inside the active layer, and to ensure efficient extraction through the charge transport layers.
KW - built-in potential
KW - charge collection
KW - charge transport layers
KW - perovskite solar cells
Y1 - 2020
U6 - https://doi.org/10.1002/admi.202000041
SN - 2196-7350
VL - 7
IS - 10
PB - Wiley
CY - Hoboken
ER -
TY - JOUR
A1 - Jiang, Wei
A1 - Tao, Chen
A1 - Stolterfoht, Martin
A1 - Jin, Hui
A1 - Stephen, Meera
A1 - Lin, Qianqian
A1 - Nagiri, Ravi C. R.
A1 - Burn, Paul L.
A1 - Gentle, Ian R.
T1 - Hole-transporting materials for low donor content organic solar cells
BT - charge transport and device performance
JF - Organic electronics : physics, materials and applications
N2 - Low donor content solar cells are an intriguing class of photovoltaic device about which there is still considerable discussion with respect to their mode of operation. We have synthesized a series of triphenylamine-based materials for use in low donor content devices with the electron accepting [6,6]-phenyl-C71-butyric acid methyl ester (PC(7)0BM). The triphenylamine-based materials absorb light in the near UV enabling the PC(7)0BM to be be the main light absorbing organic semiconducting material in the solar cell. It was found that the devices did not operate as classical Schottky junctions but rather photocurrent was generated by hole transfer from the photo-excited PC(7)0BM to the triphenylamine-based donors. We found that replacing the methoxy surface groups with methyl groups on the donor material led to a decrease in hole mobility for the neat films, which was due to the methyl substituted materials having the propensity to aggregate. The thermodynamic drive to aggregate was advantageous for the performance of the low donor content (6 wt%) films. It was found that the 6 wt% donor devices generally gave higher performance than devices containing 50 wt% of the donor.
KW - photoexcited hole transfer
KW - photocurrent generation
KW - synthesis
KW - hole
KW - mobility
KW - low donor content
KW - Schottky junction
Y1 - 2020
U6 - https://doi.org/10.1016/j.orgel.2019.105480
SN - 1566-1199
SN - 1878-5530
VL - 76
PB - Elsevier
CY - Amsterdam
ER -
TY - GEN
A1 - Wolff, Christian Michael
A1 - Canil, Laura
A1 - Rehermann, Carolin
A1 - Nguyen, Ngoc Linh
A1 - Zu, Fengshuo
A1 - Ralaiarisoa, Maryline
A1 - Caprioglio, Pietro
A1 - Fiedler, Lukas
A1 - Stolterfoht, Martin
A1 - Kogikoski, Junior, Sergio
A1 - Bald, Ilko
A1 - Koch, Norbert
A1 - Unger, Eva L.
A1 - Dittrich, Thomas
A1 - Abate, Antonio
A1 - Neher, Dieter
T1 - Correction to 'Perfluorinated self-assembled monolayers enhance the stability and efficiency of inverted perovskite solar cells' (2020, 14 (2), 1445−1456)
T2 - ACS nano
Y1 - 2020
U6 - https://doi.org/10.1021/acsnano.0c08081
SN - 1936-0851
SN - 1936-086X
VL - 14
IS - 11
SP - 16156
EP - 16156
PB - American Chemical Society
CY - Washington, DC
ER -
TY - JOUR
A1 - Kirchartz, Thomas
A1 - Márquez, José A.
A1 - Stolterfoht, Martin
A1 - Unold, Thomas
T1 - Photoluminescence-based characterization of halide perovskites for photovoltaics
JF - Advanced Energy Materials
N2 - Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials.
KW - metal halide perovskites
KW - numerical simulations
KW - photoluminescence
KW - photon recycling
Y1 - 2020
U6 - https://doi.org/10.1002/aenm.201904134
SN - 1614-6832
SN - 1614-6840
VL - 10
IS - 26
SP - 1
EP - 21
PB - Wiley
CY - Weinheim
ER -
TY - GEN
A1 - Kirchartz, Thomas
A1 - Márquez, José A.
A1 - Stolterfoht, Martin
A1 - Unold, Thomas
T1 - Photoluminescence-based characterization of halide perovskites for photovoltaics
T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1419
KW - metal halide perovskites
KW - numerical simulations
KW - photoluminescence
KW - photon recycling
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519702
SN - 1866-8372
IS - 26
ER -
TY - JOUR
A1 - Wang, Qiong
A1 - Smith, Joel A.
A1 - Skroblin, Dieter
A1 - Steele, Julian A.
A1 - Wolff, Christian Michael
A1 - Caprioglio, Pietro
A1 - Stolterfoht, Martin
A1 - Köbler, Hans
A1 - Turren-Cruz, Silver-Hamill
A1 - Li, Meng
A1 - Gollwitzer, Christian
A1 - Neher, Dieter
A1 - Abate, Antonio
T1 - Managing phase purities and crystal orientation for high-performance and photostable cesium lead halide perovskite solar cells
JF - Solar RRL
N2 - Inorganic perovskites with cesium (Cs+) as the cation have great potential as photovoltaic materials if their phase purity and stability can be addressed. Herein, a series of inorganic perovskites is studied, and it is found that the power conversion efficiency of solar cells with compositions CsPbI1.8Br1.2, CsPbI2.0Br1.0, and CsPbI2.2Br0.8 exhibits a high dependence on the initial annealing step that is found to significantly affect the crystallization and texture behavior of the final perovskite film. At its optimized annealing temperature, CsPbI1.8Br1.2 exhibits a pure orthorhombic phase and only one crystal orientation of the (110) plane. Consequently, this allows for the best efficiency of up to 14.6% and the longest operational lifetime, T-S80, of approximate to 300 h, averaged of over six solar cells, during the maximum power point tracking measurement under continuous light illumination and nitrogen atmosphere. This work provides essential progress on the enhancement of photovoltaic performance and stability of CsPbI3 - xBrx perovskite solar cells.
KW - cesium lead halides
KW - crystal orientation
KW - inorganic perovskites
KW - ISOS-L-1I protocol
KW - phase purity
KW - photostability
Y1 - 2020
VL - 4
IS - 9
PB - WILEY-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Samson, Stephanie
A1 - Rech, Jeromy
A1 - Perdigón-Toro, Lorena
A1 - Peng, Zhengxing
A1 - Shoaee, Safa
A1 - Ade, Harald
A1 - Neher, Dieter
A1 - Stolterfoht, Martin
A1 - You, Wei
T1 - Organic solar cells with large insensitivity to donor polymer molar mass across all acceptor classes
JF - ACS applied polymer materials
N2 - Donor polymer number-average molar mass (M-n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M-n effects varies from system to system, although there is generally some intermediate M-n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC61BM (fullerene acceptor), PcBm demonstrated <10% variation in power conversion efficiency and a consistent morphology over a large span of M-n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M-n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ mn insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M-n control during synthesis.
KW - polymer solar cells
KW - conjugated polymers
KW - fullerenes
KW - fluorination
KW - molecular weight
KW - non-fullerene acceptors
KW - power conversion efficiency
Y1 - 2020
U6 - https://doi.org/10.1021/acsapm.0c01041
SN - 2637-6105
VL - 2
IS - 11
SP - 5300
EP - 5308
PB - American Chemical Society
CY - Washington
ER -
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 - Raoufi, Meysam
A1 - Hörmann, Ulrich
A1 - Ligorio, Giovanni
A1 - Hildebrandt, Jana
A1 - Pätzel, Michael
A1 - Schultz, Thorsten
A1 - Perdigón-Toro, Lorena
A1 - Koch, Norbert
A1 - List-Kratochvil, Emil
A1 - Hecht, Stefan
A1 - Neher, Dieter
T1 - Simultaneous effect of ultraviolet radiation and surface modification on the work function and hole injection properties of ZnO thin films
JF - Physica Status Solidi. A , Applications and materials science
N2 - The combined effect of ultraviolet (UV) light soaking and self-assembled monolayer deposition on the work function (WF) of thin ZnO layers and on the efficiency of hole injection into the prototypical conjugated polymer poly(3-hexylthiophen-2,5-diyl) (P3HT) is systematically investigated. It is shown that the WF and injection efficiency depend strongly on the history of UV light exposure. Proper treatment of the ZnO layer enables ohmic hole injection into P3HT, demonstrating ZnO as a potential anode material for organic optoelectronic devices. The results also suggest that valid conclusions on the energy-level alignment at the ZnO/organic interfaces may only be drawn if the illumination history is precisely known and controlled. This is inherently problematic when comparing electronic data from ultraviolet photoelectron spectroscopy (UPS) measurements carried out under different or ill-defined illumination conditions.
KW - charge injection across hybrid interfaces
KW - energy-level alignments
KW - hybrid metal oxides
KW - organic interfaces
Y1 - 2020
U6 - https://doi.org/10.1002/pssa.201900876
SN - 1862-6300
SN - 1862-6319
VL - 217
IS - 5
SP - 1
EP - 6
PB - Wiley-VCH
CY - Weinheim
ER -
TY - THES
A1 - Jay, Raphael Martin
T1 - Principles of charge distribution and separation
BT - the case of iron complexes probed by X-ray spectroscopy
N2 - The electronic charge distributions of transition metal complexes fundamentally determine their chemical reactivity. Experimental access to the local valence electronic structure is therefore crucial in order to determine how frontier orbitals are delocalized between different atomic sites and electronic charge is spread throughout the transition metal complex. To that end, X-ray spectroscopies are employed in this thesis to study a series of solution-phase iron complexes with respect to the response of their local electronic charge distributions to different external influences. Using resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) at the iron L-edge, changes in local charge densities are investigated at the iron center depending on different ligand cages as well as solvent environments. A varying degree of charge delocalization from the metal center onto the ligands is observed, which is governed by the capabilities of the ligands to accept charge density into their unoccupied orbitals. Specific solvents are furthermore shown to amplify this process. Solvent molecules of strong Lewis-acids withdraw charge from the ligand allowing in turn for more metal charge to be delocalized onto the ligand. The resulting local charge deficiencies at the metal center are, however, counteracted by competing electron-donation channels from the ligand towards the iron, which are additionally revealed. This is interpreted as a compensating effect which strives to maintain local charge densities at the iron center. This mechanism of charge density preservation is found to be of general nature. Using time-resolved RIXS and XAS at the iron L-edge, an analogous interplay of electron donation and back-donation channels is also revealed for the case of charge-transfer excited states. In such transient configurations, the electronic occupation of iron-centered frontier orbitals has been altered by an optical excitation. Changes in local charge densities that are expected to follow an increased or decreased population of iron-centered orbitals are, however, again counteracted. By scaling the degree of electron donation from the ligand onto the metal, local charge densities at the iron center can be efficiently maintained. Since charge-transfer excitations, however, often constitute the initial step in many electron transfer processes, these findings challenge common notions of charge-separation in transition metal dyes.
KW - L-edge spectroscopy
KW - charge-transfer excitations
KW - transition metal complexes
KW - electronic structure
KW - photo-chemical pathways
Y1 - 2020
ER -
TY - JOUR
A1 - Cabalar, Pedro
A1 - Fandiño, Jorge
A1 - Lierler, Yuliya
T1 - Modular Answer Set Programming as a formal specification language
JF - Theory and practice of logic programming
N2 - In this paper, we study the problem of formal verification for Answer Set Programming (ASP), namely, obtaining aformal proofshowing that the answer sets of a given (non-ground) logic programPcorrectly correspond to the solutions to the problem encoded byP, regardless of the problem instance. To this aim, we use a formal specification language based on ASP modules, so that each module can be proved to capture some informal aspect of the problem in an isolated way. This specification language relies on a novel definition of (possibly nested, first order)program modulesthat may incorporate local hidden atoms at different levels. Then,verifyingthe logic programPamounts to prove some kind of equivalence betweenPand its modular specification.
KW - Answer Set Programming
KW - formal specification
KW - formal verification
KW - modular logic programs
Y1 - 2020
U6 - https://doi.org/10.1017/S1471068420000265
SN - 1471-0684
SN - 1475-3081
VL - 20
IS - 5
SP - 767
EP - 782
PB - Cambridge University Press
CY - New York
ER -
TY - THES
A1 - Köhler, Raphael
T1 - Towards seasonal prediction: stratosphere-troposphere coupling in the atmospheric model ICON-NWP
N2 - Stratospheric variability is one of the main potential sources for sub-seasonal to seasonal predictability in mid-latitudes in winter. Stratospheric pathways play an important role for long-range teleconnections between tropical phenomena, such as the quasi-biennial oscillation (QBO) and El Niño-Southern Oscillation (ENSO), and the mid-latitudes on the one hand, and linkages between Arctic climate change and the mid-latitudes on the other hand. In order to move forward in the field of extratropical seasonal predictions, it is essential that an atmospheric model is able to realistically simulate the stratospheric circulation and variability. The numerical weather prediction (NWP) configuration of the ICOsahedral Non-hydrostatic atmosphere model ICON is currently being used by the German Meteorological Service for the regular weather forecast, and is intended to produce seasonal predictions in future. This thesis represents the first extensive evaluation of Northern Hemisphere stratospheric winter circulation in ICON-NWP by analysing a large set of seasonal ensemble experiments.
An ICON control climatology simulated with a default setup is able to reproduce the basic behaviour of the stratospheric polar vortex. However, stratospheric westerlies are significantly too weak and major stratospheric warmings too frequent, especially in January. The weak stratospheric polar vortex in ICON is furthermore connected to a mean sea level pressure (MSLP) bias pattern resembling the negative phase of the Arctic Oscillation (AO). Since a good representation of the drag exerted by gravity waves is crucial for a realistic simulation of the stratosphere, three sensitivity experiments with reduced gravity wave drag are performed. Both a reduction of the non-orographic and orographic gravity wave drag respectively, lead to a strengthening of the stratospheric vortex and thus a bias reduction in winter, in particular in January. However, the effect of the non-orographic gravity wave drag on the stratosphere is stronger. A third experiment, combining a reduced orographic and non-orographic drag, exhibits the largest stratospheric bias reductions. The analysis of stratosphere-troposphere coupling based on an index of the Northern Annular Mode demonstrates that ICON realistically represents downward coupling. This coupling is intensified and more realistic in experiments with a reduced gravity wave drag, in particular with reduced non-orographic drag. Tropospheric circulation is also affected by the reduced gravity wave drag, especially in January, when the strongly improved stratospheric circulation reduces biases in the MSLP patterns. Moreover, a retuning of the subgrid-scale orography parameterisations leads to a significant error reduction in the MSLP in all months. In conclusion, the combination of these adjusted parameterisations is recommended as a current optimal setup for seasonal simulations with ICON.
Additionally, this thesis discusses further possible influences on the stratospheric polar vortex, including the influence of tropical phenomena, such as QBO and ENSO, as well as the influence of a rapidly warming Arctic. ICON does not simulate the quasi-oscillatory behaviour of the QBO and favours weak easterlies in the tropical stratosphere. A comparison with a reanalysis composite of the easterly QBO phase reveals, that the shift towards the easterly QBO in ICON further weakens the stratospheric polar vortex. On the other hand, the stratospheric reaction to ENSO events in ICON is realistic. ICON and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. To investigate the influence of Arctic climate change on mid-latitude circulation changes, two differing approaches with transient and fixed sea ice conditions are chosen. Neither ICON approach exhibits the mid-latitude tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, as it is discussed on the basis of observational evidence. Nevertheless, adding a new model to the current and active discussion on Arctic-midlatitude linkages, further contributes to the understanding of divergent conclusions between model and observational studies.
N2 - Die stratosphärische Variabilität ist eine der wichtigsten potentiellen Quellen für die Vorhersagbarkeit der atmosphärischen Zirkulation in den mittleren Breiten im Winter auf der Zeitskala von Wochen bis zu Jahreszeiten. Stratosphärische Prozesse spielen eine grundlegende Rolle für die Fernverbindungen (Telekonnektionen) zwischen tropischen Klimaphänomenen, wie der quasi-zweijährigen Schwingung (QBO) oder „El Niño-Südliche Oszillation“ (ENSO), und den mittleren Breiten, sowie den Telekonnektionen zwischen arktischen Klimaänderungen und der atmosphärischen Zirkulation in den mittleren Breiten. Die Fähigkeit eines atmosphärischen Modells, die stratosphärische Zirkulation und deren Variabilität realistisch zu simulieren, ist deshalb von grundlegender Bedeutung, um die Jahreszeitenvorhersage in den mittleren Breiten deutlich zu verbessern. Das nichthydrostatische Atmosphärenmodell ICON (ICOsahedral Non-hydrostatic atmosphere model) wird gegenwärtig beim Deutschen Wetterdienst (DWD) in der numerischen Wettervorhersagekonfiguration (ICON-NWP) für die Wettervorhersage genutzt, und soll zukünftig auch für Jahreszeitenvorhersagen benutzt werden. Darauf basierend, präsentiert die vorliegende Arbeit eine Vielzahl von saisonalen Ensembleexperimenten mit ICON-NWP und liefert damit die erste umfassende Bewertung der stratosphärischen Winterzirkulation der nördlichen Hemisphäre in ICON-NWP.
Die Klimatologie eines ICON-Modelllaufs im Standardsetup reproduziert die grundlegenden Eigenschaften des stratosphärischen Polarwirbels. Allerdings sind die stratosphärischen Westwinde deutlich schwächer als in den Beobachtungen, und starke Stratosphärenerwärmungen treten insbesondere im Januar zu häufig auf. Zudem ist der schwache stratosphärische Polarwirbel in ICON mit einem typischen Fehler-Muster des Bodenluftdrucks verknüpft, welches der negativen Phase der Arktischen Oszillation (AO) ähnelt. Da eine gute Darstellung des von Schwerewellen ausgeübten Widerstands für eine realistische Simulation der Stratosphäre entscheidend ist, werden drei Sensitivitätsexperimente mit reduziertem Schwerewellenwiderstand durchgeführt. Sowohl eine Verringerung des nicht-orographischen, als auch eine Verringerung des orographischen Schwerewellenwiderstands führen jeweils zu einer Verstärkung des stratosphärischen Wirbels und damit zu einer Verringerung des Fehlers im Winter, insbesondere im Januar. Die Wirkung des nicht-orographischen Schwerewellenwiderstands auf die Stratosphäre ist hierbei jedoch stärker. Ein drittes Experiment, welches den reduzierten orographischen und nicht-orographischen Widerstand kombiniert, zeigt die größten Verbesserungen in der Stratosphäre. Die auf dem Index des „Northern Annular Mode“ basierende Analyse der Stratosphären-Troposphären-Kopplung zeigt, dass ICON die nach unten gerichtete Kopplung zwischen der Stratosphäre und Troposphäre realistisch darstellt. Diese Kopplung wird in Experimenten mit einem reduzierten Schwerewellenwiderstand verstärkt und realistischer dargestellt, dies gilt insbesondere für den reduzierten nicht-orographischen Widerstand. Auch die troposphärische Zirkulation wird durch den reduzierten Schwerewellenwiderstand beeinflusst, vor allem im Januar, wenn die stark verbesserte stratosphärische Zirkulation den Fehler in den Bodenluftdruckfeldern reduziert. Darüber hinaus führt ein Tuning der Parameterisierung der subgrid-skaligen orographischen Schwerewellen zu einer signifikanten Fehlerreduktion des Bodenluftdrucks in allen Monaten. Die Kombination all dieser angepassten Parametrisierungen wird als derzeit optimales Setup für Jahreszeiten-Simulationen mit ICON vorgeschlagen.
Darüber hinaus werden in dieser Arbeit weitere mögliche Einflussfaktoren auf den stratosphärischen Polarwirbel diskutiert, darunter der Einfluss tropischer Phänomene, wie QBO und ENSO, sowie der Einfluss einer sich rasch erwärmenden Arktis. Das quasi-oszillierende Verhalten der QBO wird durch ICON nicht simuliert, sodass schwache Ostwinde in der tropischen Stratosphäre dominieren. Ein Vergleich mit einem Reanalyse-Komposit der östlichen QBO-Phase zeigt, dass die Verschiebung in Richtung der östlichen QBO in ICON den stratosphärischen Polarwirbel weiter abschwächt. Die stratosphärische Reaktion auf ENSO-Ereignisse in ICON ist jedoch realistisch. ICON und Reanalysedaten zeigen einen abgeschwächten Stratosphärenwirbel in warmen ENSO-Jahren. Darüber hinaus begünstigen insbesondere im Winter warme ENSO-Ereignisse die negative Phase der Arktischen Oszillation, während kalte Ereignisse die positive Phase begünstigen. Die ICON-Simulationen deuten auch auf einen signifikanten Effekt von ENSO auf den atlantisch-europäischen Sektor im Spätwinter hin. Um den Einfluss des arktischen Klimawandels auf Änderungen der Zirkulation in mittleren Breiten zu untersuchen, werden zwei unterschiedliche Ansätze mit transienten und festen Meereisgrenzen gewählt. Keiner der beiden ICON-Ansätze zeigt eine Tendenz zur negativen Phase der Arktische Oszillation als Reaktion auf die verstärkte Erwärmung der Arktis, wie sie in der Literatur anhand von Beobachtungsdaten häufig diskutiert wird. Jedoch wird somit der aktuellen und aktiven Diskussion zu den Auswirkungen des arktischen Klimawandels auf die Zirkulation der mittleren Breiten ein neues Modell hinzugefügt.
T2 - Im Hinblick auf die Jahreszeitenvorhersage: Stratosphären-Troposphären-Kopplung in dem Atmosphärenmodell ICON-NWP
KW - Seasonal prediction
KW - Stratosphere-troposphere coupling
KW - ICON
KW - Stratospheric polar vortex
KW - Jahreszeitenvorhersage
KW - Stratosphären-Troposphären-Kopplung
KW - ICON
KW - Stratosphärischer Polarwirbel
KW - El Niño-Southern Oscillation (ENSO)
KW - El Niño-Südliche Oszillation
KW - Arctic-midlatitude linkages
KW - Verbindungspfade zwischen der Arktis und den mittleren Breiten
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-487231
ER -
TY - GEN
A1 - Wang, Qiong
A1 - Smith, Joel A.
A1 - Skroblin, Dieter
A1 - Steele, Julian A.
A1 - Wolff, Christian Michael
A1 - Caprioglio, Pietro
A1 - Stolterfoht, Martin
A1 - Köbler, Hans
A1 - Turren-Cruz, Silver-Hamill
A1 - Li, Meng
A1 - Gollwitzer, Christian
A1 - Neher, Dieter
A1 - Abate, Antonio
T1 - Managing phase purities and crystal orientation for high-performance and photostable cesium lead halide perovskite solar cells
T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - Inorganic perovskites with cesium (Cs+) as the cation have great potential as photovoltaic materials if their phase purity and stability can be addressed. Herein, a series of inorganic perovskites is studied, and it is found that the power conversion efficiency of solar cells with compositions CsPbI1.8Br1.2, CsPbI2.0Br1.0, and CsPbI2.2Br0.8 exhibits a high dependence on the initial annealing step that is found to significantly affect the crystallization and texture behavior of the final perovskite film. At its optimized annealing temperature, CsPbI1.8Br1.2 exhibits a pure orthorhombic phase and only one crystal orientation of the (110) plane. Consequently, this allows for the best efficiency of up to 14.6% and the longest operational lifetime, T-S80, of approximate to 300 h, averaged of over six solar cells, during the maximum power point tracking measurement under continuous light illumination and nitrogen atmosphere. This work provides essential progress on the enhancement of photovoltaic performance and stability of CsPbI3 - xBrx perovskite solar cells.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1210
KW - cesium lead halides
KW - crystal orientation
KW - inorganic perovskites
KW - ISOS-L-1I protocol
KW - phase purity
KW - photostability
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525374
SN - 1866-8372
IS - 9
ER -
TY - JOUR
A1 - Abdalla, H.
A1 - Adam, R.
A1 - Aharonian, Felix A.
A1 - Benkhali, F. Ait
A1 - Angüner, Ekrem Oǧuzhan
A1 - Arcaro, C.
A1 - Armand, C.
A1 - Armstrong, T.
A1 - Ashkar, H.
A1 - Backes, M.
A1 - Baghmanyan, V.
A1 - Martins, V. Barbosa
A1 - Barnacka, A.
A1 - Barnard, M.
A1 - Becherini, Y.
A1 - Berge, D.
A1 - Bernlohr, K.
A1 - Bi, B.
A1 - Bottcher, M.
A1 - Boisson, C.
A1 - Bolmont, J.
A1 - de Lavergne, M. de Bony
A1 - Bordas, Pol
A1 - Breuhaus, M.
A1 - Brun, F.
A1 - Brun, P.
A1 - Bryan, M.
A1 - Buchele, M.
A1 - Bulik, T.
A1 - Bylund, T.
A1 - Caroff, S.
A1 - Carosi, A.
A1 - Casanova, Sabrina
A1 - Chand, T.
A1 - Chandra, S.
A1 - Chen, A.
A1 - Cotter, G.
A1 - Curylo, M.
A1 - Mbarubucyeye, J. Damascene
A1 - Davids, I. D.
A1 - Davies, J.
A1 - Deil, C.
A1 - Devin, J.
A1 - deWilt, P.
A1 - Dirson, L.
A1 - Djannati-Atai, A.
A1 - Dmytriiev, A.
A1 - Donath, A.
A1 - Doroshenko, V.
A1 - Duffy, C.
A1 - Dyks, J.
A1 - Egberts, Kathrin
A1 - Eichhorn, F.
A1 - Einecke, S.
A1 - Emery, G.
A1 - Ernenwein, J. -P.
A1 - Feijen, K.
A1 - Fegan, S.
A1 - Fiasson, A.
A1 - de Clairfontaine, G. Fichet
A1 - Fontaine, G.
A1 - Funk, S.
A1 - Fussling, Matthias
A1 - Gabici, S.
A1 - Gallant, Y. A.
A1 - Giavitto, G.
A1 - Giunti, L.
A1 - Glawion, D.
A1 - Glicenstein, J. F.
A1 - Gottschall, D.
A1 - Grondin, M. -H.
A1 - Hahn, J.
A1 - Haupt, M.
A1 - Hermann, G.
A1 - Hinton, J. A.
A1 - Hofmann, W.
A1 - Hoischen, Clemens
A1 - Holch, T. L.
A1 - Holler, M.
A1 - Horbe, M.
A1 - Horns, D.
A1 - Huber, D.
A1 - Jamrozy, M.
A1 - Jankowsky, D.
A1 - Jankowsky, F.
A1 - Jardin-Blicq, A.
A1 - Joshi, V.
A1 - Jung-Richardt, I.
A1 - Kasai, E.
A1 - Kastendieck, M. A.
A1 - Katarzynski, K.
A1 - Katz, U.
A1 - Khangulyan, D.
A1 - Khelifi, B.
A1 - Klepser, S.
A1 - Kluzniak, W.
A1 - Komin, Nu.
A1 - Konno, R.
A1 - Kosack, K.
A1 - Kostunin, D.
A1 - Kreter, M.
A1 - Lamanna, G.
A1 - Lemiere, A.
A1 - Lemoine-Goumard, M.
A1 - Lenain, J. -P.
A1 - Levy, C.
A1 - Lohse, T.
A1 - Lypova, I.
A1 - Mackey, J.
A1 - Majumdar, J.
A1 - Malyshev, D.
A1 - Malyshev, D.
A1 - Marandon, V.
A1 - Marchegiani, P.
A1 - Marcowith, Alexandre
A1 - Mares, A.
A1 - Marti-Devesa, G.
A1 - Marx, R.
A1 - Maurin, G.
A1 - Meintjes, P. J.
A1 - Meyer, M.
A1 - Mitchell, A.
A1 - Moderski, R.
A1 - Mohamed, M.
A1 - Mohrmann, L.
A1 - Montanari, A.
A1 - Moore, C.
A1 - Morris, P.
A1 - Moulin, Emmanuel
A1 - Muller, J.
A1 - Murach, T.
A1 - Nakashima, K.
A1 - Nayerhoda, A.
A1 - de Naurois, M.
A1 - Ndiyavala, H.
A1 - Niederwanger, F.
A1 - Niemiec, J.
A1 - Oakes, L.
A1 - O'Brien, Patrick
A1 - Odaka, H.
A1 - Ohm, S.
A1 - Olivera-Nieto, L.
A1 - Wilhelmi, E. de Ona
A1 - Ostrowski, M.
A1 - Oya, I.
A1 - Panter, M.
A1 - Panny, S.
A1 - Parsons, R. D.
A1 - Peron, G.
A1 - Peyaud, B.
A1 - Piel, Q.
A1 - Pita, S.
A1 - Poireau, V.
A1 - Noel, A. Priyana
A1 - Prokhorov, D. A.
A1 - Prokoph, H.
A1 - Puhlhofer, G.
A1 - Punch, M.
A1 - Quirrenbach, A.
A1 - Raab, S.
A1 - Rauth, R.
A1 - Reichherzer, P.
A1 - Reimer, A.
A1 - Reimer, O.
A1 - Remy, Q.
A1 - Renaud, M.
A1 - Rieger, F.
A1 - Rinchiuso, L.
A1 - Romoli, C.
A1 - Rowell, G.
A1 - Rudak, B.
A1 - Ruiz-Velasco, E.
A1 - Sahakian, V.
A1 - Sailer, S.
A1 - Sanchez, D. A.
A1 - Santangelo, Andrea
A1 - Sasaki, M.
A1 - Scalici, M.
A1 - Schussler, F.
A1 - Schutte, H. M.
A1 - Schwanke, U.
A1 - Schwemmer, S.
A1 - Seglar-Arroyo, M.
A1 - Senniappan, M.
A1 - Seyffert, A. S.
A1 - Shafi, N.
A1 - Shiningayamwe, K.
A1 - Simoni, R.
A1 - Sinha, A.
A1 - Sol, H.
A1 - Specovius, A.
A1 - Spencer, S.
A1 - Spir-Jacob, M.
A1 - Stawarz, L.
A1 - Sun, L.
A1 - Steenkamp, R.
A1 - Stegmann, C.
A1 - Steinmassl, S.
A1 - Steppa, C.
A1 - Takahashi, T.
A1 - Tavernier, T.
A1 - Taylor, A. M.
A1 - Terrier, R.
A1 - Tiziani, D.
A1 - Tluczykont, M.
A1 - Tomankova, L.
A1 - Trichard, C.
A1 - Tsirou, M.
A1 - Tuffs, R.
A1 - Uchiyama, Y.
A1 - van der Walt, D. J.
A1 - van Eldik, C.
A1 - van Rensburg, C.
A1 - van Soelen, B.
A1 - Vasileiadis, G.
A1 - Veh, J.
A1 - Venter, C.
A1 - Vincent, P.
A1 - Vink, J.
A1 - Volk, H. J.
A1 - Vuillaume, T.
A1 - Wadiasingh, Z.
A1 - Wagner, S. J.
A1 - Watson, J.
A1 - Werner, F.
A1 - White, R.
A1 - Wierzcholska, A.
A1 - Wong, Yu Wun
A1 - Yusafzai, A.
A1 - Zacharias, M.
A1 - Zanin, R.
A1 - Zargaryan, D.
A1 - Zdziarski, A. A.
A1 - Zech, Alraune
A1 - Zhu, S. J.
A1 - Ziegler, A.
A1 - Zorn, J.
A1 - Zouari, S.
A1 - Zywucka, N.
T1 - An extreme particle accelerator in the Galactic plane
BT - HESS J1826-130
JF - Astronomy and astrophysics : an international weekly journal
N2 - The unidentified very-high-energy (VHE; E > 0.1 TeV) gamma -ray source, HESS J1826-130, was discovered with the High Energy Stereoscopic System (HESS) in the Galactic plane. The analysis of 215 h of HESS data has revealed a steady gamma -ray flux from HESS J1826-130, which appears extended with a half-width of 0.21 degrees +/- 0.02
(stat)degrees
stat degrees +/- 0.05
(sys)degrees sys degrees . The source spectrum is best fit with either a power-law function with a spectral index Gamma = 1.78 +/- 0.10(stat) +/- 0.20(sys) and an exponential cut-off at 15.2
(+5.5)(-3.2) -3.2+5.5 TeV, or a broken power-law with Gamma (1) = 1.96 +/- 0.06(stat) +/- 0.20(sys), Gamma (2) = 3.59 +/- 0.69(stat) +/- 0.20(sys) for energies below and above E-br = 11.2 +/- 2.7 TeV, respectively. The VHE flux from HESS J1826-130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula, HESS J1825-137, particularly at the low end of the energy spectrum. Leptonic scenarios for the origin of HESS J1826-130 VHE emission related to PSR J1826-1256 are confronted by our spectral and morphological analysis. In a hadronic framework, taking into account the properties of dense gas regions surrounding HESS J1826-130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to greater than or similar to 200 TeV. Our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants, molecular clouds, and counterparts detected in radio, X-rays, and TeV energies.
KW - ISM: supernova remnants
KW - ISM: clouds
KW - gamma rays: general
KW - gamma rays:
KW - ISM
Y1 - 2020
U6 - https://doi.org/10.1051/0004-6361/202038851
SN - 0004-6361
SN - 1432-0746
VL - 644
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Cheng, Xin
A1 - Zhang, Jie
A1 - Kliem, Bernhard
A1 - Török, Tibor
A1 - Xing, Chen
A1 - Zhou, Zhenjun
A1 - Inhester, Bernd
A1 - Ding, Mingde
T1 - Initiation and early kinematic evolution of solar eruptions
JF - The Astrophysical Journal
N2 - We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s(-1). A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration.
KW - solar coronal mass ejections
KW - stellar coronal mass ejections
KW - solar storm
Y1 - 2020
U6 - https://doi.org/10.3847/1538-4357/ab886a
SN - 1055-6796
SN - 1476-3540
VL - 894
IS - 2
SP - 1
EP - 20
PB - Cambridge Scientific Publishers
CY - Cambridge
ER -
TY - JOUR
A1 - Cervantes Villa, Juan Sebastian
A1 - Shprits, Yuri Y.
A1 - Aseev, Nikita
A1 - Allison, Hayley J.
T1 - Quantifying the effects of EMIC wave scattering and magnetopause shadowing in the outer electron radiation belt by means of data assimilation
JF - Journal of geophysical research : Space physics
N2 - In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of radiation belt electrons by assimilating data from Van Allen Probes A and B and Geostationary Operational Environmental Satellites (GOES) 13 and 15 into a 3-D diffusion model. In particular, we examine the respective contribution of electromagnetic ion cyclotron (EMIC) wave scattering and magnetopause shadowing for values of the first adiabatic invariant mu ranging from 300 to 3,000 MeV G(-1). We inspect the innovation vector and perform a statistical analysis to quantitatively assess the effect of both processes as a function of various geomagnetic indices, solar wind parameters, and radial distance from the Earth. Our results are in agreement with previous studies that demonstrated the energy dependence of these two mechanisms. We show that EMIC wave scattering tends to dominate loss at lower L shells, and it may amount to between 10%/hr and 30%/hr of the maximum value of phase space density (PSD) over all L shells for fixed first and second adiabatic invariants. On the other hand, magnetopause shadowing is found to deplete electrons across all energies, mostly at higher L shells, resulting in loss from 50%/hr to 70%/hr of the maximum PSD. Nevertheless, during times of enhanced geomagnetic activity, both processes can operate beyond such location and encompass the entire outer radiation belt.
Y1 - 2020
U6 - https://doi.org/10.1029/2020JA028208
SN - 2169-9380
SN - 2169-9402
VL - 125
IS - 8
PB - American Geophysical Union
CY - Washington
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 - Pelisoli, Ingrid
A1 - Vos, Joris
A1 - Geier, Stephan
A1 - Schaffenroth, Veronika
A1 - Baran, Andrzej S.
T1 - Alone but not lonely
BT - observational evidence that binary interaction is always required to form hot subdwarf stars
JF - Astronomy and astrophysics : an international weekly journal
N2 - Context. Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant suffers an extreme mass-loss episode. Binary interaction is suggested to be the main formation channel, but the high fraction of apparently single hot subdwarfs (up to 30%) has prompted single star formation scenarios to be proposed.Aims. We investigate the possibility that hot subdwarfs could form without interaction by studying wide binary systems. If single formation scenarios were possible, there should be hot subdwarfs in wide binaries that have undergone no interaction.Methods. Angular momentum accretion during interaction is predicted to cause the hot subdwarf companion to spin up to the critical velocity. The effect of this should still be observable given the timescales of the hot subdwarf phase. To study the rotation rates of companions, we have analysed light curves from the Transiting Exoplanet Survey Satellite for all known hot subdwarfs showing composite spectral energy distributions indicating the presence of a main sequence wide binary companion. If formation without interaction were possible, that would also imply the existence of hot subdwarfs in very wide binaries that are not predicted to interact. To identify such systems, we have searched for common proper motion companions with projected orbital distances of up to 0.1 pc to all known spectroscopically confirmed hot subdwarfs using Gaia DR2 astrometry.Results. We find that the companions in composite hot subdwarfs show short rotation periods when compared to field main sequence stars. They display a triangular-shaped distribution with a peak around 2.5 days, similar to what is observed for young open clusters. We also report a shortage of hot subdwarfs with candidate common proper motion companions. We identify only 16 candidates after probing 2938 hot subdwarfs with good astrometry. Out of those, at least six seem to be hierarchical triple systems, in which the hot subdwarf is part of an inner binary.Conclusions. The observed distribution of rotation rates for the companions in known wide hot subdwarf binaries provides evidence of previous interaction causing spin-up. Additionally, there is a shortage of hot subdwarfs in common proper motion pairs, considering the frequency of such systems among progenitors. These results suggest that binary interaction is always required for the formation of hot subdwarfs.
KW - subdwarfs
KW - binaries: general
KW - stars: variables: general
Y1 - 2020
U6 - https://doi.org/10.1051/0004-6361/202038473
SN - 0004-6361
SN - 1432-0746
VL - 642
PB - EDP Sciences
CY - Les Ulis
ER -