Ultrathin Al2O3 Protective Layer to Stabilize the Electrochromic Switching Performance of Amorphous WOx Thin Films

Abstract Electrochromic materials play a key role in smart windows, displays or anti‐glare rear‐view mirrors. Tungsten oxide is an intensely studied representative due to its extraordinary coloring performance. For commercial use, however, further optimization of the general cycle stability as well as the protection against external factors, such as moisture, is a still ongoing focus of research. In this study, the stabilization of the electrochromic switching performance of tungsten oxide is investigated using an ultrathin optimized Al2O3 protective coating, grown by atomic layer deposition. Amorphous tungsten oxide (a‐WOx) thin films are prepared by reactive radio‐frequency sputtering. The composition as well as electronic structure of the pure a‐WOx films is studied by X‐ray photoelectron spectroscopy. The electrochromic properties of the multilayer system are investigated in a nonaqueous electrolyte as well as in an electrolyte containing 10 vol% water. On the basis of these results, the stabilizing effect on the electrochromic switching characteristics of a‐WOx by the use of the additional thin Al2O3 protective layer is evident. It is shown that degradation and ageing of a‐WOx due to moisture can be prevented and coloration efficiencies of 50.4 cm2 C−1 can be achieved at 630 nm

Study of defects in electron irradiated CuInSe2 by positron lifetime spectroscopy

CuInSe2 was studied in the as-grown state and after low-temperature (4 K) 2 MeV electron irradiation. The positron bulk lifetime of 235 ps was measured for the unirradiated sample. The positron bulk lifetime was theoretically calculated and is in good agreement with the experimental value. In addition, the defect-related lifetimes for mono-, di-, and trivacancies are theoretically determined. An increased average positron lifetime indicated after electron irradiation the appearance of open-volume defects, most probably of divacancy type. The disappearance of this defect was observed during annealing below 250 K. Other defects were formed leading to a divacancy signal at least stable up to 600 K in the temperature range above 450 K.Peer reviewe

Reaction Mechanism and Surface Film Formation of Conversion Materials for Lithium- and Sodium-Ion Batteries: An XPS Case Study on Sputtered Copper Oxide (CuO) Thin Film Model Electrodes

Charge storage based on conversion reactions is a promising concept to store electrical energy. Many studies have been devoted to conversion reactions with lithium; however, still many scientific questions remain due to the complexity of the reaction mechanism combined with surface film formation. Replacing lithium by sodium is an attractive approach to widen the scope of conversion reactions and to study whether the increase in ion size changes the reaction mechanisms and whether the cell performance benefits or worsens. In this study, we use thin film electrodes as a additive-free model system to study the conversion reaction of CuO with sodium (CuO/Na) by means of electrochemical methods, microscopy, and X-ray photoelectron spectroscopy. The reaction mechanism and film formation are being discussed. Some important differences to the analogue lithium-based system (CuO/Li) are found. Whereas CuO has been reported as charge product in CuO/Li cells, charging is incomplete in the case of CuO/Na and only Cu₂O is formed. As an important finding, oxygen appears to be redox active and Na₂O₂ forms during charging from Na₂O. Moreover, surface film formation due to electrolyte decomposition is much more severe as compared to CuO/Li. Depth profiling is used to probe the inner composition of the surface film, revealing a much thicker surface film with more inorganic components as compared to the lithium system. It is also found that the surface film disappears to a large extent during charging