High-Temperature Anodized WO₃ Nanoplatelet Films for Photosensitive Devices

Abstract

Anodization at elevated temperatures in nitric acid has been used for the production of highly porous and thick tungsten trioxide nanostructured films for photosensitive device applications. The anodization process resulted in platelet crystals with thicknesses of 20-60 nm and lengths of 100-1000 nm. Maximum thicknesses of approximately 2.4 microm were obtained after 4 h of anodization at 20 V. X-ray diffraction analysis revealed that the as-prepared anodized samples contain predominantly hydrated tungstite phases depending on voltage, while films annealed at 400 degrees C for 4 h are predominantly orthorhombic WO3 phase. Photocurrent measurements revealed that the current density of the 2.4 microm nanostructured anodized film was 6 times larger than the nonanodized films. Dye-sensitized solar cells developed using these films produced 0.33 V and 0.65 mA/cm2 in open- and short-circuit conditions.

Honey-Comb Structured WO3/TiO2Thin Films with Improved Electrochromic Properties

“…• C is a commonly observed structure which has been also reported by Sadek et al 27 and Judeinstein et al 28 when they studied the influence of annealing on the phase transformations of WO 3 at this temperature.…”

TiO2 Nanotubes: Synthesis and Applications

“…Other extremes may be non-valve metals, such as iron, where high-aspect-ratio oxide structures were reported only very recently, [364][365][366] or WO 3 structures, for which still no highly ordered and only comparably short tube structures were reported. [353,355,[368][369][370] The main reasons for this different behavior can be ascribed to following factors: 1) the solubility of a formed oxide structure in the anodizing electrolyte affects the aspect ratio, 2) the solubility of the fluoride species (or any other sensitizer) at cell boundaries affects tube or pore morphology and the observation of sidewall ripples, 3) different Pilling-Bedworth ratios that affect stress that is generated when the oxide is formed, thus the adhesion of the tube layer to the substrate or the tube length (overshoot by plastic flow) and the self-organization length scale are also affected.…”

TiO2‐Nanoröhren: Synthese und Anwendungen

“…Das andere Extrem findet sich bei Nichtventilmetallen wie Fe, für das erst vor kurzem über Oxidstrukturen mit hohem Aspektverhältnis berichtet wurde, [364][365][366] oder bei WO 3 -Strukturen, für die bisher noch keine hoch geordneten und nur vergleichsweise kurze Röhrenstrukturen bekannt sind. [353,355,[368][369][370] Die wesentlichen Ursachen für dieses unterschiedliche Verhalten kann folgenden Faktoren zugeschrieben werden: 1) Die Löslichkeit einer gebildeten Oxidstruktur im anodisierenden Elektrolyt beeinflusst das Aspektverhältnis. 2) Die Löslichkeit der Fluoridspezies (oder anderer Sensibilisatoren) an Zellgrenzen beeinflusst die Röhren-oder Porenmorphologie sowie die Beobachtung von Wellen an den Röhrenaußenwänden.…”