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- ItemAmorphous-Like Ultralow Thermal Transport in Crystalline Argyrodite Cu7PS6(Weinheim : Wiley-VCH, 2024) Shen, Xingchen; Ouyang, Niuchang; Huang, Yuling; Tung, Yung‐Hsiang; Yang, Chun‐Chuen; Faizan, Muhammad; Perez, Nicolas; He, Ran; Sotnikov, Andrei; Willa, Kristin; Wang, Chen; Chen, Yue; Guilmeau, EmmanuelDue to their amorphous-like ultralow lattice thermal conductivity both below and above the superionic phase transition, crystalline Cu- and Ag-based superionic argyrodites have garnered widespread attention as promising thermoelectric materials. However, despite their intriguing properties, quantifying their lattice thermal conductivities and a comprehensive understanding of the microscopic dynamics that drive these extraordinary properties are still lacking. Here, an integrated experimental and theoretical approach is adopted to reveal the presence of Cu-dominated low-energy optical phonons in the Cu-based argyrodite Cu7PS6. These phonons yield strong acoustic-optical phonon scattering through avoided crossing, enabling ultralow lattice thermal conductivity. The Unified Theory of thermal transport is employed to analyze heat conduction and successfully reproduce the experimental amorphous-like ultralow lattice thermal conductivities, ranging from 0.43 to 0.58 W m−1 K−1, in the temperature range of 100–400 K. The study reveals that the amorphous-like ultralow thermal conductivity of Cu7PS6 stems from a significantly dominant wave-like conduction mechanism. Moreover, the simulations elucidate the wave-like thermal transport mainly results from the contribution of Cu-associated low-energy overlapping optical phonons. This study highlights the crucial role of low-energy and overlapping optical modes in facilitating amorphous-like ultralow thermal transport, providing a thorough understanding of the underlying complex dynamics of argyrodites.
- ItemSymmetry‐Induced Selective Excitation of Topological States in Su–Schrieffer–Heeger Waveguide Arrays(Weinheim : Wiley-VCH, 2023) Tang, Min; Wang, Jiawei; Valligatla, Sreeramulu; Saggau, Christian N.; Dong, Haiyun; Saei Ghareh Naz, Ehsan; Klembt, Sebastian; Lee, Ching Hua; Thomale, Ronny; van den Brink, Jeroen; Fulga, Ion Cosma; Schmidt, Oliver G.; Ma, LiboThe investigation of topological state transition in carefully designed photonic lattices is of high interest for fundamental research, as well as for applied studies such as manipulating light flow in on-chip photonic systems. Herein, the topological phase transition between symmetric topological zero modes (TZM) and antisymmetric TZMs in Su–Schrieffer–Heeger mirror symmetric waveguides is reported. The transition of TZMs is realized by adjusting the coupling ratio between neighboring waveguide pairs, which is enabled by selective modulation of the refractive index in the waveguide gaps. Bidirectional topological transitions between symmetric and antisymmetric TZMs can be achieved with proposed switching strategy. Selective excitation of topological edge mode is demonstrated owing to the symmetry characteristics of the TZMs. The flexible manipulation of topological states is promising for on-chip light flow control and may spark further investigations on symmetric/antisymmetric TZM transitions in other photonic topological frameworks.
- ItemNd─Nd Bond in Ih and D5h Cage Isomers of Nd2@C80 Stabilized by Electrophilic CF3 Addition(Weinheim : Wiley-VCH, 2023) Yang, Wei; Velkos, Georgios; Rosenkranz, Marco; Schiemenz, Sandra; Liu, Fupin; Popov, Alexey A.Synthesis of molecular compounds with metal–metal bonds between 4f elements is recognized as one of the fascinating milestones in lanthanide metallochemistry. The main focus of such studies is on heavy lanthanides due to the interest in their magnetism, while bonding between light lanthanides remains unexplored. In this work, the Nd─Nd bonding in Nd-dimetallofullerenes as a case study of metal–metal bonding between early lanthanides is demonstrated. Combined experimental and computational study proves that pristine Nd2@C80 has an open shell structure with a single electron occupying the Nd─Nd bonding orbital. Nd2@C80 is stabilized by a one-electron reduction and further by the electrophilic CF3 addition to [Nd2@C80]−. Single-crystal X-ray diffraction reveals the formation of two Nd2@C80(CF3) isomers with D5h-C80 and Ih-C80 carbon cages, both featuring a single-electron Nd─Nd bond with the length of 3.78–3.79 Å. The mutual influence of the exohedral CF3 group and endohedral metal dimer in determining the molecular structure of the adducts is analyzed. Unlike Tb or Dy analogs, which are strong single-molecule magnets with high blocking temperature of magnetization, the slow relaxation of magnetization in Nd2@Ih-C80(CF3) is detectable via out-of-phase magnetic susceptibility only below 3 K and in the presence of magnetic field.
- ItemElucidating Structure Formation in Highly Oriented Triple Cation Perovskite Films(Weinheim : Wiley-VCH, 2023) Telschow, Oscar; Scheffczyk, Niels; Hinderhofer, Alexander; Merten, Lena; Kneschaurek, Ekaterina; Bertram, Florian; Zhou, Qi; Löffler, Markus; Schreiber, Frank; Paulus, Fabian; Vaynzof, YanaMetal halide perovskites are an emerging class of crystalline semiconductors of great interest for application in optoelectronics. Their properties are dictated not only by their composition, but also by their crystalline structure and microstructure. While significant efforts are dedicated to the development of strategies for microstructural control, significantly less is known about the processes that govern the formation of their crystalline structure in thin films, in particular in the context of crystalline orientation. This work investigates the formation of highly oriented triple cation perovskite films fabricated by utilizing a range of alcohols as an antisolvent. Examining the film formation by in situ grazing-incidence wide-angle X-ray scattering reveals the presence of a short-lived highly oriented crystalline intermediate, which is identified as FAI-PbI2-xDMSO. The intermediate phase templates the crystallization of the perovskite layer, resulting in highly oriented perovskite layers. The formation of this dimethylsulfoxide (DMSO) containing intermediate is triggered by the selective removal of N,N-dimethylformamide (DMF) when alcohols are used as an antisolvent, consequently leading to differing degrees of orientation depending on the antisolvent properties. Finally, this work demonstrates that photovoltaic devices fabricated from the highly oriented films, are superior to those with a random polycrystalline structure in terms of both performance and stability.
- ItemMechanically Stable, Binder‐Free, and Free‐Standing Vanadium Trioxide/Carbon Hybrid Fiber Electrodes for Lithium‐Ion Batteries(Weinheim : Wiley-VCH, 2023) Bornamehr, Behnoosh; Gallei, Markus; Husmann, Samantha; Presser, VolkerBinder is a crucial component in present-day battery electrodes but commonly contains fluorine and requires coating processing using organic (often toxic) solvents. Preparing binder-free electrodes is an attractive strategy to make battery electrode production and its end-of-use waste greener and safer. Herein, electrospinning is employed to prepare binder-free and self-standing electrodes. Such electrodes often suffer from low flexibility, and the correlation between performance and flexibility is usually overlooked. Processing parameters affect the mechanical properties of the electrodes, and for the first time it is reported that mechanical flexibility directly influences the electrochemical performance of the electrode. The importance is highlighted when processing parameters advantageous to powder materials, such as a higher heat treatment temperature, harm self-standing electrodes due to deterioration of fiber flexibility. Other strategies, such as conductive carbon addition, can be employed to improve the cell performance, but their effect on the mechanical properties of the electrodes must be considered. Rapid heat treatment achieves self-standing V2O3 with a capacity of 250 mAh g−1 at 250 mA g−1 and 390 mAh g−1 at 10 mA g−1
- ItemPhotoluminescence Mapping over Laser Pulse Fluence and Repetition Rate as a Fingerprint of Charge and Defect Dynamics in Perovskites(Weinheim : Wiley-VCH, 2023) Rao, Shraddha M.; Kiligaridis, Alexander; Yangui, Aymen; An, Qingzhi; Vaynzof, Yana; Scheblykin, Ivan G.Defects in metal halide perovskites (MHP) are photosensitive, making the observer effect unavoidable when laser spectroscopy methods are applied. Photoluminescence (PL) bleaching and enhancement under light soaking and recovery in dark are examples of the transient phenomena that are consequent to the creation and healing of defects. Depending on the initial sample composition, environment, and other factors, the defect nature and evolution can strongly vary, making spectroscopic data analysis prone to misinterpretations. Herein, the use of an automatically acquired dependence of PL quantum yield (PLQY) on the laser pulse repetition rate and pulse fluence as a unique fingerprint of both charge carrier dynamics and defect evolution is demonstrated. A simple visual comparison of such fingerprints allows for assessment of similarities and differences between MHP samples. The study illustrates this by examining methylammonium lead triiodide (MAPbI3) films with altered stoichiometry that just after preparation showed very pronounced defect dynamics at time scale from milliseconds to seconds, clearly distorting the PLQY fingerprint. Upon weeks of storage, the sample fingerprints evolve toward the standard stoichiometric MAPbI3 in terms of both charge carrier dynamics and defect stability. Automatic PLQY mapping can be used as a universal method for assessment of perovskite sample quality.
- ItemSemitransparent Perovskite Solar Cells with an Evaporated Ultra-Thin Perovskite Absorber(Weinheim : Wiley-VCH, 2023) Zhang, Zongbao; Ji, Ran; Jia, Xiangkun; Wang, Shu‐Jen; Deconinck, Marielle; Siliavka, Elena; Vaynzof, YanaMetal halide perovskites are of great interest for application in semitransparent solar cells due to their tunable bandgap and high performance. However, fabricating high-efficiency perovskite semitransparent devices with high average visible transmittance (AVT) is challenging because of their high absorption coefficient. Here, a co-evaporation process is adopted to fabricate ultra-thin CsPbI3 perovskite films. The smooth surface and orientated crystal growth of the evaporated perovskite films make it possible to achieve 10 nm thin films with compact and continuous morphology without pinholes. When integrated into a p-i-n device structure of glass/ITO/PTAA/perovskite/PCBM/BCP/Al/Ag with an optimized transparent electrode, these ultra-thin layers result in an impressive open-circuit voltage (VOC) of 1.08 V and a fill factor (FF) of 80%. Consequently, a power conversion efficiency (PCE) of 3.6% with an AVT above 50% is demonstrated, which is the first report for a perovskite device of a 10 nm active layer thickness with high VOC, FF and AVT. These findings demonstrate that deposition by thermal evaporation makes it possible to form compact ultra-thin perovskite films, which are of great interest for future smart windows, light-emitting diodes, and tandem device applications.
- ItemA Highly Active Cobalt Catalyst for the General and Selective Hydrogenation of Aromatic Heterocycles(Weinheim : Wiley-VCH, 2023) Bauer, Christof; Müller, Felix; Keskin, Sercan; Zobel, Mirijam; Kempe, RhettNanostructured earth abundant metal catalysts that mediate important chemical reactions with high efficiency and selectivity are of great interest. This study introduces a synthesis protocol for nanostructured earth abundant metal catalysts. Three components, an inexpensive metal precursor, an easy to synthesize N/C precursor, and a porous support material undergo pyrolysis to give the catalyst material in a simple, single synthesis step. By applying this catalyst synthesis, a highly active cobalt catalyst for the general and selective hydrogenation of aromatic heterocycles could be generated. The reaction is important with regard to organic synthesis and hydrogen storage. The mild reaction conditions observed for quinolines permit the selective hydrogenation of numerous classes of N-, O- and S-heterocyclic compounds such as: quinoxalines, pyridines, pyrroles, indoles, isoquinoline, aciridine amine, phenanthroline, benzofuranes, and benzothiophenes.
- ItemOn the Preparation and Spectroelectrochemical Characterization of Certain 2,5-Bis(het)aryl Substituted Thiophenes(Weinheim : Wiley-VCH, 2024) Dmitrieva, Evgenia; Barche, Jens; Popov, Alexey A.; Hartmann, HorstIn this work, a series of novel 2,5-bis(het)aryl and 2,5-bis-thienyl substituted thiophenes have been synthesized and characterized by ultraviolet-visible-near infrared (UV-Vis-NIR) absorption and fluorescence spectroscopy as well as cyclic voltammetry. From the electron paramagnetic resonance (EPR)/UV-Vis-NIR spectroelectrochemical data, information about the optical and magnetic properties of the charged species of these compounds have been provided. The spin distributions in the electrochemically generated radical ions were estimated experimentally and compared with theoretical data.
- ItemGelation Kinetics and Mechanical Properties of Thiol-Tetrazole Methylsulfone Hydrogels Designed for Cell Encapsulation(Weinheim : Wiley-VCH, 2022) de Miguel‐Jiménez, Adrián; Ebeling, Bastian; Paez, Julieta I.; Fink‐Straube, Claudia; Pearson, Samuel; del Campo, AránzazuHydrogel precursors that crosslink within minutes are essential for the development of cell encapsulation matrices and their implementation in automated systems. Such timescales allow sufficient mixing of cells and hydrogel precursors under low shear forces and the achievement of homogeneous networks and cell distributions in the 3D cell culture. The previous work showed that the thiol-tetrazole methylsulfone (TzMS) reaction crosslinks star-poly(ethylene glycol) (PEG) hydrogels within minutes at around physiological pH and can be accelerated or slowed down with small pH changes. The resulting hydrogels are cytocompatible and stable in cell culture conditions. Here, the gelation kinetics and mechanical properties of PEG-based hydrogels formed by thiol-TzMS crosslinking as a function of buffer, crosslinker structure and degree of TzMS functionality are reported. Crosslinkers of different architecture, length and chemical nature (PEG versus peptide) are tested, and degree of TzMS functionality is modified by inclusion of RGD cell-adhesive ligand, all at concentration ranges typically used in cell culture. These studies corroborate that thiol/PEG-4TzMS hydrogels show gelation times and stiffnesses that are suitable for 3D cell encapsulation and tunable through changes in hydrogel composition. The results of this study guide formulation of encapsulating hydrogels for manual and automated 3D cell culture.
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