Multi-Color Electrochromism in Vanadium Oxide Thin Films

Abstract

To date, numerous researchers have spent great efforts in searching for transition metal oxides with diverse properties. Vanadium oxide are a family of interesting materials with high catalytic, electrical, optical and magnetic properties and potential applications such as thermochromic smart windows, batteries and electrochromic devices[1-2]. In this study, vanadium oxide thin films were deposited by two techniques, namely, reactive RF magnetron sputtering and Doctor Blade leading to V2O5 films with a wide range of optical properties. RF sputtered films deposited in gas mixture of argon and oxygen at room temperature on ITO substrates crystallized in an orthorhombic structure when using a V metal target while they were amorphous from V2O5 target. Depending on the deposition conditions, the film morphology was layer or needle type. Orthorhombic V2O5 thin fims were prepared by Doctor Blade deposition on ITO substrate from V2O5 powder synthesized by polyol process[3-4]. Independently of the deposition technique, the electrochromic properties of vanadium oxide films showed multi steps electrochromism, namely yellow to green, green to blue, and blue to grey, in lithium based electrolyte. The optical transmittance characterized by UV-visible spectrophotometer showed a maximum difference of 40% at 550 nm for RF sputtered films while a contrast in reflectance of 20%, in the spectral region 550-700nm, was recorded for Doctor Blade films. The influence of lithium insertion/desinsertion in the structure and chemical state was investigated using GIXD and XPS analysis. The relationship between the film structure, morphology, thickness, correlated with their deposition conditions and the EC mechanism will be discussed. References Cao Z and Wei B, V2O5/single-walled carbon nanotube hybrid mesoporous films as cathodes with high-rate capacities for recharge able lithium ion batteries, Nano Energy 2, 481 (2013). Yaoming Sun et al., Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties, Scientific Reports, 3, 2756 (2013). I. Mjejri, L. Manceriu, M. Gaudon, A. Rougier, F. Sediri, Solid State Ionics, 292 8-14 (2016). I. Mjejri, A; Rougier, M. Gaudon, Inorganic Chemistry, Submitted.