Electrochromism of vanadium oxide films doped by rare-earth (Pr, Nd, Sm, Dy) oxides

To enhance the electrochromism of vanadium oxide films used as a counter electrode of tungsten oxide (WO3) films in electrochromic (EC) devices, VM (Pr, Nd, Sm, Dy) oxide films were synthesized by vacuum evaporation and annealed at 400 °C. The effects of 25% rare earth addition on electrochromism, structure and optical properties of the vanadium oxide films were investigated. By using cyclic voltammetry, it was found that all VM (Pr, Nd, Sm, Dy) oxide films heated at 400 °C for 30 min showed ten times better cycling stabilities in PC solution than vanadium oxide films. In situ UV–vis–NIR spectroelectrochemical measurements confirmed that all VM oxide films had higher transmittances than vanadium oxide film under the colored state in vis and NIR. Of the VM oxide films, VSm oxide film showed a very small coloration efficiency (CE; 0.6) in vis and NIR, and showed good ionic and electronic conduction, implying its potential application as a counter electrode in EC devices. From XRD results, the formation of orthovanadate SmVO4 and DyVO4 was testified in VSm and VDy oxide films, respectively. Moreover, a close relationship between the doping effects of M3+ and its radius was found.