Liebe Leserinnen und Leser, insbesondere liebe Lehrerinnen und Lehrer, Fridays for Future, Geneditierung im menschlichem Embryo oder die Impfdebatte: aktuelle Themen stoßen bei Schülern offensichtlich auf großes Interesse und liefern oft eine Steilvorlage für den Unterricht. Da bietet es sich doch an, einen Experten einzuladen oder eine Universität zu besuchen. Regelmäßig ist das kaum machbar: zu hoch die Kosten, zu groß der Organisationsaufwand, zu voll der Lehrplan. Viel einfacher und außerdem kostenlos wäre ein virtueller Besuch, ein Gespräch live per Webvideokonferenz! So entstand die Plattform www.ring-a-scientist.org. Mehr als 80 Wissenschaftler sind aktuell auf Ring-a-Scientist registriert – vom Bachelorstudenten zur Professorin, vom Slavisten zur Informatikerin. In zehn verschiedenen Sprachen beteiligen sie sich an Debatten im Unterricht, geben Einblick in aktuelle Forschung, unterstützen bei der Berufswahl, zeigen Experimente und geben Führungen durch Labore – alles virtuell und live per Webcam. Die Experten stehen auf Abruf für den Unterricht zur Verfügung: Über ein einfaches Kontaktformular können sie – mit minimalem Organisationsaufwand ganz nach Wünschen der Lehrenden – in den Unterricht eingeladen werden. Auch einige Scientists-for-Future sind inzwischen dabei: Diese unterstützen die Fridays-for-Future Bewegung aktiv und können im Unterricht Fakten zur Klimadebatte liefern. Ihre Profile sind entsprechend mit dem Scientists-for-Future-Logo gekennzeichnet. Webvideokonferenzen gehören ohnehin zum Alltag in der Wissenschaft. Virtuelle Besuche sparen Zeit. Nicht zuletzt deshalb finden wir so viele Kollegen, die für diese Art der Kommunikation sehr offen sind. Und die Videokonferenzen zeigen: Gerade die Schüler scheinen sich in der virtuellen Kommunikation wohl zu fühlen, stellen Fragen, die im direkten Gespräch vielleicht unangenehm wären. Wir können Schüler im ländlichen Raum erreichen und Experimente zeigen, die man nicht ins Klassenzimmer hätte transportieren können. So bekamen wir beispielsweise die Anfrage einer Lehrerin, die sich im Biologieunterricht mit dem Thema DNA-Sequenzierung beschäftigte. Sie fand auf der Plattform eine Wissenschaftlerin, die die Methode in ihrem Unterricht mit einer Live-Demo eines Sequenziergeräts veranschaulichen konnte. Trotzdem soll das virtuelle Gespräch Schulbesuche ergänzen und niemals ersetzen. Die Vision: Ring-a-Scientist will Wissenschaftler und Lehrer weltweit vernetzen, Wissenschaftlern das Kommunizieren erleichtern und Schülern reale Vorbilder zeigen. Vielleicht entsteht so ein Fenster im Elfenbeinturm der Universitäten und ein Gegenpol zu Populismus und „Fake News“. Projekte wie Ring-a-Scientist (und viele andere) können dazu beitragen, dass aktuelle Forschung ihren Weg an die Schulen findet. Dann wird Wissenschaft als Prozess erlebbar. Ein Verständnis für aktuelle Themen macht Schüler und Schülerinnen zu mündigen Bürgern, die die Chancen und Risiken zukunftsweisender Technologien im gesellschaftlichen Dialog verantwortungsvoll abwägen können. Langfristig sollen aber nicht nur Schulen von Ring-a-Scientist profitieren, denn Web-Videokonferenzen mit Wissenschaftlern lassen sich auch anderweitig einsetzen: Im Museum zum Beispiel waren Forschende von Ring-a-Scientist schon als „Live-Exponat“ zu sehen. Eine Hürde bleibt jedoch bestehen: Nicht alle Schulen verfügen über eine ausreichende Internetverbindung. Laut einer Studie der Bertelsmann Stiftung aus dem Jahr 2017 haben 20 Prozent der Schulen kein WLAN und nur gut 30 Prozent sind mit der WLAN-Qualität zufrieden. Das muss sich ändern! Bildung im 21. Jahrhundert verdient Technologie des 21. Jahrhunderts. Zum Schluss richten wir uns mit einer Bitte an Sie, liebe Leserinnen und Leser: Wir würden uns freuen, wenn noch mehr Lehrer das Angebot von Ring-a-Scientist nutzen würden. Danke für jede Anfrage und jeden „Schneeball“, der die Plattform an Schulen bekannter macht. Ihre Kerstin Göpfrich und Ihr Karl Gödel Kerstin Göpfrich ist wissenschaftliche Mitarbeiterin am Max-Planck-Institut für medizinische Forschung, Karl C. Gödel Entwicklungsingenieur bei der Robert Bosch GmbH. Gemeinsam etablierten sie Ring-a-Scientist (www.ring-a-scientist.org).

The efficacy with which solvent vapor annealing (SVA) can control block copolymer self-assembly has so far been demonstrated primarily for the simplest class of copolymer, the linear diblock copolymer. Adding a third distinct block-thereby creating a triblock terpolymer-not only provides convenient access to complex continuous network morphologies, particularly the gyroid phases, but also opens up a route toward the fabrication of novel nanoscale devices such as optical metamaterials. Such applications, however, require the generation of well-ordered 3D continuous networks, which in turn requires a detailed understanding of the SVA process in terpolymer network morphologies. Here, in situ grazing-incidence small-angle X-ray scattering (GISAXS) is employed to study the self-assembly of a gyroid-forming triblock terpolymer during SVA, revealing the effects of several key SVA parameters on the morphology, lateral order, and, in particular, its preservation in the dried film. The robustness of the terpolymer gyroid morphology is a key requirement for successful SVA, allowing the exploration of annealing parameters which may enable the generation of films with long-range order, e.g., for optical metamaterial applications.

Fundamental understanding of the charge transport physics of hybrid lead halide perovskite semiconductors is important for advancing their use in high-performance optoelectronics. We use field-effect transistors (FETs) to probe the charge transport mechanism in thin films of methylammonium lead iodide (MAPbI3). We show that through optimization of thin-film microstructure and source-drain contact modifications, it is possible to significantly minimize instability and hysteresis in FET characteristics and demonstrate an electron field-effect mobility (μFET) of 0.5 cm2/Vs at room temperature. Temperature-dependent transport studies revealed a negative coefficient of mobility with three different temperature regimes. On the basis of electrical and spectroscopic studies, we attribute the three different regimes to transport limited by ion migration due to point defects associated with grain boundaries, polarization disorder of the MA+ cations, and thermal vibrations of the lead halide inorganic cages.

We investigate the effect of a post heat treatment of the absorber layer in air for antimony sulfide (Sb2S3) sensitized solar cells. Phenomenologically, exposing the Sb2S3 surface of sensitised solar cells to air at elevated temperatures is known to improve device performance. Here, we have investigated the detailed origins of this improvement. To this end, samples were annealed in air for different time periods and the build-up of an antimony oxide layer was monitored by XPS. A very short heat treatment resulted in an increase in power conversion efficiency from η = 1.4% to η = 2.4%, while longer annealing decreased the device performance. This improvement was linked to a reduction in charge carrier recombination at the interface of Sb2S3 with the organic hole conductor, arising from the oxide barrier layer, as demonstrated by intensity modulated photovoltage spectroscopy (IMVS).

Low-bandgap CH3 NH3 (Pbx Sn1-x )I3 (0 ≤ x ≤ 1) hybrid perovskites (e.g., ≈1.5-1.1 eV) demonstrating high surface coverage and superior optoelectronic properties are fabricated. State-of-the-art photovoltaic (PV) performance is reported with power conversion efficiencies approaching 10% in planar heterojunction architecture with small (<450 meV) energy loss compared to the bandgap and high (>100 cm2 V-1 s-1 ) intrinsic carrier mobilities.

╓*@Θ| xû└*@ oƒUfJ½*@. s║, &û*@ ÿºsE) ü*@ ª I* Sl*@ Y√;█ úW*@ Ñá█ K* C*@ ïo (|╢.*@■ φ▓ _w**@*┘▓|]**@¢ s≡ Lh≥*@│ Cⁿ├ û▐*@ MI╓ ßΦ╩*@ jä~ ª^╖*@ íh*└" ƒ*@* δ* µï*@ σ (@*╠ x*@.¿ oÖ╙ e*@*╧╜ çKN*@ zΣ**₧;*@ 7»: r $*@─╢ EÖ**@ R╤ X√;√*@ Σ≤ èº* Θ*@ 4╫ iñÑ╥*@┤ pYà═└*@⌐ kφ}¬¬*@£┌* ª╢ ö*@ ÜÜ* oHâ*@*│ ùmºm*@ t** 4X*@┬▌ Y╗ φB*@ èT*[* 2*@ 3¿ 68***@│ DgÖE**@»: rñ≤*@* Ω░┬-▀*@ 5Æ* ß╩*@ Ö╓ ª▒╜╢*@╒% π*╔₧*@ 6Å├■ è*@ N╙ g*\w*@* xßc*@ q*>? îP*@* ß_* ì9*@ É* &î&*@╙·[*≡**@> û> tA²*@, Ü╬ N* τ*@≥│ æδª╘*@ αƒR%╩╛*@÷* 2:⌐*@╦¥ Ö8ù*@╕ σ#) Θü*@░*╢-╩ l*@┤? Pn█ W*@╝ ö║ d* C*@╣ πM~ ï.*@» ΘAA)**@ Åo∩*⌠**@ XuV*∞±*@■ Ç***▐*@ üÆ**╩*@┴ É╒¡₧│*@ 3SZ Ká*@ qΣü╚" ì*@ Cq╟¢ ⁿv*@ C╦║, d*@ o*¡* mN*@ σb

We describe a new thin film deposition method for the growth of crystalline SbSI micro-needles via the conversion of Sb2S3 using SbI3 vapour, in a facile process that takes less than 15 minutes. These films were used to construct photodetectors in a sandwich-type architecture, which are superior to previously reported SbSI photodetectors. The devices exhibit a detectivity of D* = 10(9) Jones, a signal-to-noise ratio greater than SNR = 10(3) and a responsivity of R = 10(-5) A W-1. In time response measurements, raise and fall times of less than 8 ms and 34 ms were determined. This manufacturing method greatly simplifies the creation of fast photodetectors.

B. Roose, Dr. B. D. Wilts, Prof. U. Steiner, Dr. A. Abate Adolphe Merkle Institute Chemin des Verdiers 4, CH-1700 Fribourg , Switzerland E-mail: Antonio.abate@epfl .ch ; antonioabate83@gmail.com K. C. Gödel, Dr. A. Sadhanala Cavendish Laboratory Department of Physics University of Cambridge J. J. Thomson Avenue , Cambridge CB3 0HE , UK Dr. S. Pathak, Prof. H. J. Snaith Clarendon Laboratory Department of Physics University of Oxford Parks Road , Oxford OX1 3PU , UK Dr. J. P. Correa Baena, Prof. M Grätzel, Dr. A. Abate Swiss Federal Institute of Technology (EPFL) Laboratory of Photonics and Interfaces Station 6, CH-1015 Lausanne , Switzerland Prof. U. Wiesner Materials Science and Engineering Cornell University Ithaca , NY 14853 , USA

Block-copolymer templated chemical solution deposition is used to prepare mesoporous Nd-doped TiO2 electrodes for perovskite-based solar cells. X-ray diffraction and photothermal deflection spectroscopy show substitutional incorporation into the TiO2 crystal lattice for low Nd concentration, and increasing interstitial doping for higher concentrations. Substitutional Nd-doping leads to an increase in stability and performance of perovskite solar cells by eliminating defects and thus increasing electron transport and reducing charge recombination in the mesoporous TiO2. The optimized doping concentration of 0.3% Nd enables the preparation of perovskite solar cells with stabilized power conversion effi ciency of > 18%.

In lead halide perovskite solar cells, there is at least one recycling event of electron-hole pair to photon to electron-hole pair at open circuit under solar illumination. This can lead to a significant reduction in the external photoluminescence yield from the internal yield. Here we show that, for an internal yield of 70%, we measure external yields as low as 15% in planar films, where light out-coupling is inefficient, but observe values as high as 57% in films on textured substrates that enhance out-coupling. We analyse in detail how externally measured rate constants and photoluminescence efficiencies relate to internal recombination processes under photon recycling. For this, we study the photo-excited carrier dynamics and use a rate equation to relate radiative and non-radiative recombination events to measured photoluminescence efficiencies. We conclude that the use of textured active layers has the ability to improve power conversion efficiencies for both LEDs and solar cells.

Perovskite solar cells are a promising new technology for large scale energy applications. The current major challenge for commercialization is increasing the device lifetime under real working conditions. State-of-the-art perovskite solar cells are prepared using TiO2 as electron selective contact. In sealed devices, however, a reversible UV light activated performance degradation mechanism was observed. In this study, it is demonstrated that replacing TiO2 with a SnO2 electron selective contact enables stable perovskite solar cells working under UV light in an inert atmosphere. Contrary to previous reports on SnO2 based perovskite solar cells, it is shown that a mesoporous electron selective contact is required to achieve UV stable perovskite solar cells.

Sb2S3 sensitized solar cells are a promising alternative to devices employing organic dyes. The manufacture of Sb2S3 absorber layers is however slow and cumbersome. Here, we report the modified aqueous chemical bath synthesis of Sb2S3 absorber layers for sensitized solar cells. Our method is based on the hydrolysis of SbCl3 to complex antimony ions decelerating the reaction at ambient conditions, in contrast to the usual low temperature deposition protocol. This simplified deposition route allows the manufacture of sensitized mesoporous-TiO2 solar cells with power conversion efficiencies up to η = 5.1%. Photothermal deflection spectroscopy shows that the sub-bandgap trap-state density is lower in Sb2S3 films deposited with this method, compared to standard deposition protocols.

Recently, solution-processable organic-inorganic metal halide perovskites have come to the fore as a result of their high power-conversion efficiencies (PCE) in photovoltaics, exceeding 17%. To attain reproducibility in the performance, one of the critical factors is the processing conditions of the perovskite film, which directly influences the photophysical properties and hence the device performance. Here we study the effect of annealing parameters on the crystal structure of the perovskite films and correlate these changes with its photophysical properties. We find that the crystal formation is kinetically driven by the annealing atmosphere, time and temperature. Annealing in air produces an improved crystallinity and large grain domains as compared to nitrogen. Lower photoluminescence quantum efficiency (PLQE) and shorter photoluminescence (PL) lifetimes are observed for nitrogen annealed perovskite films as compared to the air-annealed counterparts. We note that the limiting nonradiative pathways (i.e., maximizing PLQE) is important for obtaining the highest device efficiency. This indicates a critical impact of the atmosphere upon crystallization and the ultimate device performance.

The performance of quantum dots (QDs) in optoelectronic devices suffers as a result of sub-bandgap states induced by the large fraction of atoms on the surface of QDs. Recent progress in passivating these surface states with thiol ligands and halide ions has led to competitive efficiencies. Here, we apply a hybrid ligand mixture to passivate PbSe QD sub-bandgap tail states via a low-temperature, solid-state ligand exchange. We show that this ligand mixture allows tuning of the energy levels and the physical QD size in the solid state during film formation. We hereby present a novel, postsynthetic path to tune the properties of QD films.

Solution-processed organo-lead halide perovskites are produced with sharp, color-pure electroluminescence that can be tuned from blue to green region of visible spectrum (425-570 nm). This was accomplished by controlling the halide composition of CH3NH3Pb(BrxCl1-x)3 [0 ≤ x ≤ 1] perovskites. The bandgap and lattice parameters change monotonically with composition. The films possess remarkably sharp band edges and a clean bandgap, with a single optically active phase. These chloride-bromide perovskites can potentially be used in optoelectronic devices like solar cells and light emitting diodes (LEDs). Here we demonstrate high color-purity, tunable LEDs with narrow emission full width at half maxima (FWHM) and low turn on voltages using thin-films of these perovskite materials, including a blue CH3NH3PbCl3 perovskite LED with a narrow emission FWHM of 5 nm.

Reversible photo‐induced performance deterioration is observed in mesoporous TiO 2 ‐containing devices in an inert environment. This phenomenon is correlated with the activation of deep trap sites due to astoichiometry of the metal oxide. Interestingly, in air, these defects can be passivated by oxygen adsorption. These results show that the doping of TiO 2 with aluminium has a striking impact upon the density of sub‐gap states and enhances the conductivity by orders of magnitude. Dye‐sensitized and perovskite solar cells employing Al‐doped TiO 2 have increased device efficiencies and significantly enhanced operational device stability in inert atmospheres. This performance and stability enhancement is attributed to the substitutional incorporation of Al in the anatase lattice, “permanently” passivating electronic trap sites in the bulk and at the surface of the TiO 2 .

Organometallic lead-halide perovskite-based solar cells now approach 18% efficiency. Introducing a mixture of bromide and iodide in the halide composition allows tuning of the optical bandgap. We prepare mixed bromide-iodide lead perovskite films CH3NH3Pb(I1-xBrx)3 (0 ≤ x ≤ 1) by spin-coating from solution and obtain films with monotonically varying bandgaps across the full composition range. Photothermal deflection spectroscopy, photoluminescence, and X-ray diffraction show that following suitable fabrication protocols these mixed lead-halide perovskite films form a single phase. The optical absorption edge of the pure triiodide and tribromide perovskites is sharp with Urbach energies of 15 and 23 meV, respectively, and reaches a maximum of 90 meV for CH3NH3PbI1.2Br1.8. We demonstrate a bromide-iodide lead perovskite film (CH3NH3PbI1.2Br1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with crystalline silicon devices.

A simulation framework for coherent X-ray imaging, based on scalar diffraction theory, is presented. It contains a core C++ library and an additional Python interface. A workflow is presented to include contributions of inelastic scattering obtained with Monte-Carlo methods. X-ray Talbot-Lau interferometry is the primary focus of the framework. Simulations are in agreement with measurements obtained with such an interferometer. Especially, the dark-field signal of densely packed PMMA microspheres is predicted. A realistic modeling of the microsphere distribution, which is necessary for correct results, is presented. The framework can be used for both setup design and optimization but also to test and improve reconstruction methods.