Study on electrochromic performances of amorphous WO3 films

A series Of WO3 films are prepared by rf-sputtering under different partial pressures of oxygen. It is found that the films with oxygen partial pressure ratio 1:10 have better electrochronic (EC) properties than others. Microstructural and compositional characteristics of WO3 films are studied by x-ray diffraction, atomic force microscopy and x-ray photo electro spectroscopy. It is obvious that the samples are amorphous and have more pores that are beneficial for Li+ to inject and eject. The original-state films are composed of tungsten and oxygen. After electrochemical reactions, the main component becomes LixWO3 in which tungsten ions normally exhibit both W6+ and W5+ oxidation states. The films are annealed in air at 230 and 400degreesC for 90 min. The cyclic voltammograms and optical transmittance show that the films annealed at 400degreesC after more than 10 cycles present better EC properties.