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Hybrid Aromatic Fluoro Amine Modified SnO2 Electron Transport Layers in Perovskite Solar Cells for Enhanced Efficiency and Stability
No full textSnO2 is a widely used electron transporting layer in perovskite solar cells. Despite the high compatibility with the perovskite absorber layers the presence of traps at the perovskite SnO2 interface results in performance losses, hence their modification to improve the performance and stability of PSCs is therefore important. In this study, we enhanced the SnO2 ETL by incorporating a bi functional aromatic amino fluorine molecule into the SnO2 precursor solution. The fluorine molecule was found to partially substitute the Sn and alter the energy levels while the aniline group aided in regulating the nucleation growth rate of the perovskite crystalline films. In this work, a hole transporting material free carbon based PSCs CPSCs was fabricated. We found that perovskite absorber layers deposited on these modified SnO2 hybrid layers have higher optoelectronic quality, resulting in enhanced photovoltaic performance, device stability, and reduced hysteresis in CPSCs. Devices made with the modified hybrid SnO2 layers exhibited PCEs of 15.6 significantly better than unmodified SnO2 with 13.5 . CPSCs with these modified SnO2 films also exhibited remarkable retention of 88.7 of their initial power conversion efficiency for a shelf life period ISOS D1I exceeding 1200 h. This study presents a generic approach to enhance the stability and performance of CPSCs by modifying the properties of the electron transport layer and, consequently, regulating the quality of the perovskite materia
Emergence of monolayer electron behavior in bulk van der Waals superlattice
No full textMonolayer transition metal dichalcogenides TMDs have a simple crystal structure, but they exhibit intricate physical phenomena that differ from their bulk counterparts. Recently, there has been significant interest in the electronic behavior of monolayer TMDs hosted in a natural van der Waals superlattice material, Ba6 amp; 8290;Nb11 amp; 8290;S28, consisting of alternating NbS2 monolayers and block layers. Here, we report the electronic structure study of Ba6 amp; 8290;Nb11 amp; 8290;S28 and Ba6 amp; 8290;Ta11 amp; 8290;S28. Using angle resolved photoemission spectroscopy and density functional theory calculation, we show that the electronic structures of the superlattices are similar to those of monolayer TMDs. The two dimensional characteristics indicate that the interlayer coupling of adjacent TMD layers is suppressed by the intercalation of the Ba3 amp; 8290;NbS5 or Ba3 amp; 8290;TaS5 block layer. A clear band splitting due to spin orbital coupling is observed in Ba6 amp; 8290;Ta11 amp; 8290;S28, while no obvious splitting is found in Ba6 amp; 8290;Nb11 amp; 8290;S28. These observations are in qualitative agreement with the observation on monolayer films of NbS2 and TaS2. Based on our findings, these natural superlattices can serve as an effective model system for studying monolayer materials and their potential application
Peri Tetracene from 1,1 Bitetracene Zipping up Structurally Defined Graphene Nanoribbons
Get PDFPolycyclic aromatic hydrocarbons PAHs are promising molecules for a manifold of applications in organic electronics, spintronics, or energy storage devices. Among PAHs, particular attention has been focused on the synthesis and study of acenes and fused acenes, peri acenes, allowing tuning of the highest occupied molecular orbital lowest unoccupied molecular orbital HOMO LUMO gap with the size of the conjugated system. As a starting point for the surface synthesis of larger PAHs, we synthesized a 1,1 amp; 8242; bitetracene for the first time. This precursor molecule consists of two tetracene units connected via the 1,1 amp; 8242; position with a torsion angle of 70 . The interface properties of the molecule before and after annealing on a Cu 111 surface are investigated. Using X ray photoemission spectroscopy XPS , angle resolved photoelectron spectroscopy ARPES , low energy electron diffraction LEED , and scanning tunneling microscopy STM , it is experimentally demonstrated that the tetracene units zip up with the help of heat forming peri tetracene. These results and the exact adsorption geometry are in excellent agreement with calculations using density functional theory DFT . Moreover, the calculations enable the identification of newly formed valence band states at the interface to Cu 11
Phase transitions in NiO during the Oxygen Evolution Reaction assessed via electrochromic phenomena through operando UV Vis spectroscopy
No full textDue to its high activity and stability, nickel oxide NiO has shown significant promise as an electrocatalyst for the alkaline oxygen evolution reaction OER . In parallel, NiO exhibits a well known electrochromic phenomenon, changing its optical properties in response to an applied electric potential. This study investigates the relationship between NiO phase changes that occur during the OER and the connected optical modulation using operando UV visible reflectance spectroscopy. The correlation between the OER activity and the electrochromic behavior of NiO is explored, providing insights into the underlying physicochemical mechanisms governing both phenomena. Strong reduction of the reflected light at higher applied potentials cannot be attributed solely to the change in optical bandgap due to the phase change or the change in the material s refractive index when different phases form. Therefore, in gap states responsible for increasing the absorption at higher applied potentials were experimentally characterized by ultraviolet photoelectron spectroscopy UPS and X ray absorption spectroscopy XAS . The results show that phase changes in NiO during OER influence its optical absorption characteristics, which in turn give access to following active phase changes of the electrocatalyst material through a non invasive, optical, operando probe in real time allowing for kinetic studies of the involved solid state conversion reaction
Laboratory soft X ray setup for transient absorption experiments in the liquid phase using a laser produced plasma source
Get PDFWith time resolved soft X ray spectroscopy, the element specific dynamics of the electronic structure of disordered systems can be investigated. Measurements of species in dilute liquid solutions are particularly challenging and require high photon flux combined with low experimental noise. This mostly limited these experiments to large scale facilities, especially for energies above the water window 533 eV . Based on a laser produced plasma source, our system enables, to the best of our knowledge, the first static and transient experiments in the liquid phase to be performed in the laboratory for energies up to 1400 eV and with a time resolution of 500 ps. We benchmark the system with static investigations of [Ni CN 4]2 amp; 8722; and transient experiments on the widely used model complex [Fe bpy 3]2 , both in an aqueous solution. The introduced self referencing concept ensures that the measurements are photon noise limited. Our results form the basis for further liquid phase experiments investigating the dynamics in diluted solution
Enhanced Surface Determination beyond Photoemission via Auger Photoelectron Coincidence Spectroscopy
Get PDFThe study of surface properties at the nanoscale plays a crucial role in material science applications. This paper demonstrates the capabilities of Auger PhotoElectron Coincidence Spectroscopy APECS to obtain data with varying surface sensitivities from a single measurement. This makes it possible to extract the spectrum from the outermost surface layer even when faced with strongly overlapping surface and bulk spectral features, which we demonstrate by accurately extracting the surface component in Au 4f photoemission. Leveraging high energy resolution, transmission efficiency, tunable photon energy, and remarkable surface sensitivity of the APECS setup, we propose that optimal experimental conditions can be tailored to determine surface spectra accurately for a diverse range of materials. This opens new avenues for advancing our understanding of nanoscale surface phenomena across various material system
Understanding Advanced Transition Metal Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering
Get PDFNon noble transition metal TM based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction 2e amp; 8722; ORR process. To efficiently drive this reaction, these TM based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non noble TM based compounds for 2e amp; 8722; ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e amp; 8722; ORR performance selectivity, activity, and stability of TM based catalysts, accompanied by an insightful exploration of the phase performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non noble TM based electrocatalyst
Understanding quantum machine learning also requires rethinking generalization
Get PDFQuantum machine learning models have shown successful generalization performance even when trained with few data. In this work, through systematic randomization experiments, we show that traditional approaches to understanding generalization fail to explain the behavior of such quantum models. Our experiments reveal that state of the art quantum neural networks accurately fit random states and random labeling of training data. This ability to memorize random data defies current notions of small generalization error, problematizing approaches that build on complexity measures such as the VC dimension, the Rademacher complexity, and all their uniform relatives. We complement our empirical results with a theoretical construction showing that quantum neural networks can fit arbitrary labels to quantum states, hinting at their memorization ability. Our results do not preclude the possibility of good generalization with few training data but rather rule out any possible guarantees based only on the properties of the model family. These findings expose a fundamental challenge in the conventional understanding of generalization in quantum machine learning and highlight the need for a paradigm shift in the study of quantum models for machine learning task
Anomalous thermal expansion and enhanced magnetocaloric effect in lt;001 gt; textured MnxFe5 xSi3 alloys
No full textThe development of zero and negative thermal expansion i.e., ZTE and NTE materials is of crucial importance to the control of undesirable thermal expansion for high precision devices. In the present work, ZTE and NTE were obtained in directionally solidified MnxFe5 xSi3 alloys with a strong amp; 8201; lt;001 gt; amp; 8201;texture, in striking contrast to positive thermal expansion in their isotropic counterparts. Magnetometry and in situ X ray diffraction XRD measurements were performed to uncover the origin of the anomalous thermal expansion. Magnetic measurements indicate a strong easy plane magnetocrystalline anisotropy in the textured samples, where the magnetic moments are aligned within the ab plane of the hexagonal structure. Temperature dependent XRD on the x amp; 8201; amp; 8201;1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition. As a result, the macroscopic ZTE amp; 8201;0.22 amp; 8201; amp; 8201;10 6 K amp; 8722;1 in the x amp; 8201; amp; 8201;1 sample can be attributed to the microscopic magneto volume effect within the ab plane, which is realized by the introduction of the amp; 8201; lt;001 gt; textured microstructure. Besides, the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x amp; 8201; amp; 8201;1.5 and 2 samples. Additionally, textured x amp; 8201; amp; 8201;1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly oriented grains. Consequently, this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotrop
Fully printed flexible perovskite solar modules with improved energy alignment by tin oxide surface modification
Get PDFFully printed flexible perovskite solar cells f PSCs show great potential for the commercialization of perovskite photovoltaics owing to their compatibility with high throughput roll to roll R2R production. However, the challenge remains in the deficiency in controlling interfacial recombination losses of the functional layer, causing remarkable loss of power conversion efficiency PCE in industrial production. Here, a fullerene substituted alkylphosphonic acid dipole layer is introduced between the R2R printed tin oxide electron transport layer and the perovskite active layer to reduce the energetic barrier and to suppress surface recombination at the buried interface. The resulting f PSCs exhibit a PCE of 17.0 with negligible hysteresis, retain 95 of their initial PCE over 3000 bending cycles and achieve a T95 lifetime of 1200 h under 1 sun and 65 C in nitrogen atmosphere. Moreover, the fully printed flexible perovskite solar mini modules f PSMs with a 20.25 cm2 aperture area achieve a PCE of 11.6 . The encapsulated f PSMs retain 90 of their initial PCE after 500 h damp heat testing at 65 C and 85 relative humidity ISOS D3 . This work marks an important progress toward the realization of efficient and stable flexible perovskite photovoltaics for commercializatio