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390 results on '"Pfeifer, Lukas"'

1. Surface passivation of FAPbI3-rich perovskite with caesium iodide outperforms bulk incorporation

Author

Baumeler, Thomas P., Alharbi, Essa A., Kakavelakis, George, Fish, George C., Aldosari, Mubarak T., Albishi, Miqad S., Pfeifer, Lukas, Carlsen, Brian I., Yum, Jun-Ho, Alharbi, Abdullah S., Mensi, Mounir D., Gao, Jing, Eickemeyer, Felix T., Sivula, Kevin, Moser, Jacques-Edouard, Zakeeruddin, Shaik M., and Graetzel, Michael

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Metal halide perovskites (MHPs) have shown an incredible rise in efficiency, reaching as high as 25.7%, which now competes with traditional photovoltaic technologies. Herein, we excluded CsX and RbX, the most commonly used cations to stabilize FAPbI3, from the bulk of perovskite thin films and applied them on the surface, as passivation agents. Extensive device optimization led to a power conversion efficiency (PCE) of 24.1% with a high fill factor (FF) of 82.2% upon passivation with CsI. We investigated in-depth the effect of CsI passivation on structural and optoelectronic properties using X-ray diffraction (XRD), angle resolved X-ray photoelectron spectroscopy (ARXPS), Kelvin Probe Force (KPFM) microscopy, time-resolved photoluminescence (TRPL), photoluminescence quantum yield (PLQY) and electroabsorption spectroscopy (TREAS). Furthermore, passivated devices exhibit enhanced operational stability, with optimized passivation with CsI leading to a retention of ~90% of initial PCE under 1 Sun illumination with maximum power point tracking for 600 h., Comment: 27 pages, 19 figures

Published
2023

4. Improving the operational stability of perovskite solar cells with cesium-doped graphene oxide interlayer

Author

Almalki, Masaud, Anagnostou, Katerina, Rogdakis, Konstantinos, Eickemeyer, Felix T., Othman, Mostafa, Stylianakis, Minas M., Tsikritzis, Dimitris, Alanazi, Anwar Q., Tzoganakis, Nikolaos, Pfeifer, Lukas, Therisod, Rita, Mo, Xiaoliang, Wolff, Christian M., Hessler-Wyser, Aïcha, Zakeeruddin, Shaik M., Zhang, Hong, Kymakis, Emmanuel, and Grätzel, Michael

Published
2024
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9. Cooperative passivation of perovskite solar cells by alkyldimethylammonium halide amphiphiles

Author

Alharbi, Essa A., Krishna, Anurag, Lempesis, Nikolaos, Dankl, Mathias, Mosquera-Lois, Irea, Hope, Michael A., Baumeler, Thomas P., Kakavelakis, George, Mishra, Aditya, Eickemeyer, Felix T., Ouellette, Olivier, Chawanpunyawat, Thanyarat, Hagfeldt, Anders, Zakeeruddin, Shaik M., Emsley, Lyndon, Pfeifer, Lukas, Roethlisberger, Ursula, and Grätzel, Michael

Published
2023
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14. New methods and reagents for carbon-fluorine bond formation

Author

Pfeifer, Lukas and Gouverneur, Véronique

Subjects
547, Chemistry, Organic, Hydrogen Bonding, Transition Metal Catalysis, Nucleophilic Fluorination, Electrophilic Fluorination
Abstract

After a general introduction about the properties and preparation of organofluorine compounds (Chapter 1), this thesis is divided into two parts focussing on the development of new methods for C-F bond formation (Part A) as well as studies towards the development of novel fluorinating reagents (Part B). Part A: New Methods for Carbon-Fluorine Bond Formation Part A consists of two chapters outlining the development of a Pd-catalysed hydrofluorination of alkenylarenes (Chapter 2) as well as a halofluorination of alkynes (Chapter 3). Chapter 2 This chapter describes the development of a novel, regioselective, syn-specific hydrofluorination of alkenylarenes under Pd-catalysis leading to the formation of benzylic fluorides. An extensive substrate scope is presented together with a model of the catalytic cycle, based on observations during the development of this reaction, deuterium labelling experiments as well as mechanistic control experiments starting from isolated palladacycles. Chapter 3 In this chapter the development of a novel iodo- as well as bromofluorination of internal and terminal alkynes, leading to the formation of (E)-halofluoroalkenes, is presented. For the former substrate class, the effects of steric as well as electronic bias on regioselectivity are discussed. For the latter substrate class, this methodology could be extended to the corresponding double iodofluorination, and for both transformations it was found to exclusively lead to the fluorination of the internal carbon. An extensive substrate scope as well as different iodofluorination-cross-coupling sequences including Suzuki, Sonogashira and Ullmann couplings, are illustrated. A representative reaction was successfully carried out on gram-scale and an iodofluorination-Suzuki-coupling sequence was used to prepare a fluorinated tamoxifen derivative. Part B: Hydrogen-Bonded Fluoride Complexes as Novel Reagents for Carbon-Fluorine Bond Formation Part B consists of two chapters describing structural as well as reactivity studies of fluoride-alcohol (Chapter 4) and fluoride-urea complexes (Chapter 5). Chapter 4 In this chapter the synthesis of 19 novel hydrogen-bonded tetraalkylammonium fluoride-alcohol complexes is described. For a subset of 15, the solid-state structures as determined by single-crystal X-ray diffraction experiments are presented. Trends of reactivity and selectivity were determined using these complexes as sources of fluoride anion in a model SN2 reaction. Preliminary results from in silico modelling of the fluoride-alcohol system provide a basis for explaining the results. Chapter 5 This chapter summarises the synthesis and solid-state structures of 20 hydrogen-bonded fluoride complexes using the urea and related squaramide and amide motifs. Also, the size of the tetraalkylammonium counter-cation was varied to study the influence on the solid-state structure. The reactivity and selectivity of a series of complexes was studied using the same model SN2 reaction as in Chapter 4 and results were compared accordingly. Different UV-vis and NMR spectroscopic techniques were used to study the behaviour of the fluoride-urea system in solution. Preliminary results demonstrate the use of 1,3-diarylureas as organocatalysts for nucleophilic fluorination.

Published
2016

24. Coupled Rotary and Oscillatory Motion in a Second-Generation Molecular Motor Pd Complex

Author

Pfeifer, Lukas, Stindt, Charlotte N., Feringa, Ben L., and Synthetic Organic Chemistry

Subjects
visible-light, Colloid and Surface Chemistry, speed, General Chemistry, rotation, Biochemistry, rotor motion, driven, Catalysis
Abstract

Molecular machines offer many opportunities for the development of responsive materials and introduce autonomous motion in molecular systems. While basic molecular switches and motors carry out one type of motion upon being exposed to an external stimulus, the development of molecular systems capable of performing coupled motions is essential for the development of more advanced molecular machinery. Overcrowded alkene-based rotary molecular motors are an ideal basis for the design of such systems as they undergo a controlled rotation initiated by light allowing for excellent spatio-temporal precision. Here, we present an example of a Pd complex of a second-generation rotary motor whose Pd center undergoes a coupled oscillatory motion relative to the motor core upon rotation of the motor. We have studied this phenomenon by UV-vis, NMR, and density functional theory calculations to support our conclusions. With this demonstration of a coupled rotation-oscillation motion powered by a light-driven molecular motor, we provide a solid basis for the development of more advanced molecular machines integrating different types of motion in their operation.

Published
2023
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25. Accuracy of polyp characterization by artificial intelligence and endoscopists: a prospective, non-randomized study in a tertiary endoscopy center

Author

Baumer, Sebastian, primary, Streicher, Kilian, primary, Alqahtani, Saleh A., additional, Brookman-Amissah, Dominic, additional, Brunner, Monika, additional, Federle, Christoph, additional, Muehlenberg, Klaus, additional, Pfeifer, Lukas, additional, Salzberger, Andrea, additional, Schorr, Wolfgang, additional, Zustin, Jozef, additional, and Pech, Oliver, additional

Published
2023
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32. Surface Passivation of FAPbI3-Rich Perovskite with Cesium Iodide Outperforms Bulk Incorporation

Author

Baumeler, Thomas P., primary, Alharbi, Essa A., additional, Kakavelakis, George, additional, Fish, George C., additional, Aldosari, Mubarak T., additional, Albishi, Miqad S., additional, Pfeifer, Lukas, additional, Carlsen, Brian I., additional, Yum, Jun-Ho, additional, Alharbi, Abdullah S., additional, Mensi, Mounir D., additional, Gao, Jing, additional, Eickemeyer, Felix T., additional, Sivula, Kevin, additional, Moser, Jacques-E, additional, Zakeeruddin, Shaik M., additional, and Grätzel, Michael, additional

Published
2023
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33. Fern cell walls and the evolution of arabinogalactan proteins in streptophytes

Author

Mueller, Kim-Kristine, Pfeifer, Lukas; https://orcid.org/0000-0002-7076-4597, Schuldt, Lina, Szövényi, Péter; https://orcid.org/0000-0002-0324-4639, de Vries, Sophie, de Vries, Jan; https://orcid.org/0000-0003-3507-5195, Johnson, Kim L, Classen, Birgit; https://orcid.org/0000-0003-1452-801X, Mueller, Kim-Kristine, Pfeifer, Lukas; https://orcid.org/0000-0002-7076-4597, Schuldt, Lina, Szövényi, Péter; https://orcid.org/0000-0002-0324-4639, de Vries, Sophie, de Vries, Jan; https://orcid.org/0000-0003-3507-5195, Johnson, Kim L, and Classen, Birgit; https://orcid.org/0000-0003-1452-801X

Abstract

Significant changes have occurred in plant cell wall composition during evolution and diversification of tracheophytes. As the sister lineage to seed plants, knowledge on the cell wall of ferns is key to track evolutionary changes across tracheophytes and to understand seed plant-specific evolutionary innovations. Fern cell wall composition is not fully understood, including limited knowledge of glycoproteins such as the fern arabinogalactan proteins (AGPs). Here, we characterize the AGPs from the leptosporangiate fern genera Azolla, Salvinia, and Ceratopteris. The carbohydrate moiety of seed plant AGPs consists of a galactan backbone including mainly 1,3- and 1,3,6-linked pyranosidic galactose, which is conserved across the investigated fern AGPs. Yet, unlike AGPs of angiosperms, those of ferns contained the unusual sugar 3-O-methylrhamnose. Besides terminal furanosidic arabinose, Ara (Araf), the main linkage type of Araf in the ferns was 1,2-linked Araf, whereas in seed plants 1,5-linked Araf is often dominating. Antibodies directed against carbohydrate epitopes of AGPs supported the structural differences between AGPs of ferns and seed plants. Comparison of AGP linkage types across the streptophyte lineage showed that angiosperms have rather conserved monosaccharide linkage types; by contrast bryophytes, ferns, and gymnosperms showed more variability. Phylogenetic analyses of glycosyltransferases involved in AGP biosynthesis and bioinformatic search for AGP protein backbones revealed a versatile genetic toolkit for AGP complexity in ferns. Our data reveal important differences across AGP diversity of which the functional significance is unknown. This diversity sheds light on the evolution of the hallmark feature of tracheophytes: their elaborate cell walls.

Published
2023

39. Tautomeric Mixture Coordination Enables Efficient Lead-Free Perovskite LEDs

Author

Wang, Ning, primary, Han, Dongyuan, additional, Wang, Jie, additional, Agosta, Lorenzo, additional, Zang, Ziang, additional, Zhao, Bin, additional, Kong, Lingmei, additional, Lu, Haizhou, additional, Mosquera-Lois, Irea, additional, Carnevali, Virginia, additional, Dong, Jianchao, additional, Zhou, Jianheng, additional, Ji, Huiyu, additional, Pfeifer, Lukas, additional, Zakeeruddin, Shaik, additional, Yang, Yingguo, additional, Wu, Bo, additional, Rothlisberger, Ursula, additional, Yang, Xuyong, additional, and Graetzel, Michael, additional

Published
2023
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49. Controlling forward and backward rotary molecular motion on demand

Author

Pfeifer, Lukas, Crespi, Stefano, Meulen, P. van der, Kemmink, J., Scheek, R.M., Hilbers, Michiel F., Buma, W.J., Feringa, B.L., Pfeifer, Lukas, Crespi, Stefano, Meulen, P. van der, Kemmink, J., Scheek, R.M., Hilbers, Michiel F., Buma, W.J., and Feringa, B.L.

Abstract

Contains fulltext : 250167.pdf (Publisher’s version ) (Open Access)

Published
2022

50. Mechanistic Insight into Supramolecular Polymerization in Water Tunable by Molecular Geometry

Author

Xu, Fan, Crespi, Stefano, Pfeifer, Lukas, Stuart, Marc C. A., Feringa, Ben L., Xu, Fan, Crespi, Stefano, Pfeifer, Lukas, Stuart, Marc C. A., and Feringa, Ben L.

Abstract

Supramolecular self-assembly in water based on non-covalent bonding is attracting major attention due to the potential of hydrogels and aqueous polymers in biomedical applications. Although supramolecular polymerization in organic solvents is well established, the key design features, the assembly mechanisms in water and achieving control over the aggregate structures remain challenging. Here, we present the assembly and disassembly of geometrical isomers of a stiff-stilbene bis-urea amphiphile (SA) in pure water. A remarkable feature of this system is that the (E)-isomer forms supramolecular polymers in both pure water and organic solvents. Taking advantage of this unique property, the hydrophobic effect was studied by comparing the supramolecular assembly in both systems. The assembly process in water follows an enthalpy-driven nucleation-elongation (cooperative) supramolecular polymerization mechanism with a standard Gibbs free energy (Delta G degrees = -53 kJ mol(-1)) double the value of the one found in toluene. We attributed this distinctive feature to the hydrophobic effect in water. Furthermore, we discovered an isomer-dependent assembly process, which can be used to control aggregation in aqueous media. Due to the substantial geometric difference between (E)-SA and (Z)-SA, we compared their assembly in water to study the influence of different driving forces involved in the process. The supramolecular polymerization of (E)-SA was cooperatively influenced by hydrogen bonding, pi-stacking, and hydrophobic effects, whereas the assembly of (Z)-SA was mainly driven by hydrophobic effects. As a result, the fiber length of (E)-SA in water is much longer than that of (Z)-SA, presenting opportunities for geometrical control of aggregation in aqueous media. [GRAPHICS]

Published
2022
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