Construction and characterization of tunable meso-/macroporous tungsten oxide-based transmissive electrochromic devices

• Published in: Journal of materials science 2009-12, Vol.44 (24), p.6608-6616
• Main Authors: Balaji, Subramanian, Djaoued, Yahia, Albert, André-Sébastien, Ferguson, Richard Z., Brüning, Ralf, Su, Bao-Lian
• Format: Article
• Language: English
• Subjects: Bleaching; Calcination; Characterization and Evaluation of Materials; Classical Mechanics; Construction; Crystallites; Crystallography and Scattering Methods; Devices; Electrochromic cells; Electrochromism; Intercalation; Lithium; Materials Science; Mesostructured Materials; Microscopy; Phase transformations; Phase transitions; Polymer Sciences; Raman spectroscopy; Roasting; Scanning electron microscopy; Solid Mechanics; Thin films; Transition metal oxides; Transition metals; Transmission electron microscopy; Tungsten oxides; X-ray diffraction
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-009-3575-8

Recent developments in the processing of porous transition metal oxide thin films have opened up new opportunities in the construction of electrochromic (EC) devices with enhanced properties. Tungsten oxide (WO 3 ) is one of the most promising materials for EC devices. In this work, we report on the synthesis of meso-/macroporous WO 3 thin films using tungstic acid as precursor and organically modified silane (ORMOSIL) as a templating agent. Calcination of the film at 500 °C resulted in nanocrystalline monoclinic tungsten oxide (m-WO 3 ) with crystallite sizes of ~16 nm. The meso-/macroporous structure is retained after calcination. An asymmetric EC device based on the meso-/macroporous m-WO 3 thin film was constructed. Thus constructed EC device was characterized by micro-Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction (XRD). Detailed micro-Raman and XRD studies of the intercalation and deintercalation of lithium (Li) in the meso-/macroporous m-WO 3 layer of the EC device as a function of the applied voltage were performed. The meso-/macroporous WO 3 layer, which was found to be monoclinic before Li intercalation, transforms to its higher symmetric phase of tetragonal and toward cubic phase when Li is intercalated into it. Upon complete deintercalation, these phase transitions were reversed and m-WO 3 is recovered. Optical transmission studies were performed in conjunction with Raman and XRD studies. This study shows that meso-/macroporous m-WO 3 layer-based EC device exhibit a high color contrast during the coloration and bleaching.