Electrochromic properties of amorphous and crystalline WO3 thin films prepared by thermal evaporation technique

The tungsten trioxides thin films were deposited by thermal evaporation method onto indium tin oxides coated onto glass substrates. The structural properties of the films were investigated by X-ray diffractometer and atomic force microscopy techniques. The as-deposited film shows a polycrystalline nature related to indium tin oxides planes and the WO3 planes appears by annealing film to 773 K for 2 h. The 2D and 3D images were carried out using atomic force microscopy techniques. The film color is converted from transparent to deep blue color after applying electric field, and bleaching occurs by applying reverse electric field. The F-like color centers model was used to investigate the coloration in amorphous films. On the other hand, the crystalline films were characterized by the free carrier absorption mechanism. Both coloration response and coloration efficiency for the amorphous films are greater than crystalline. The coloration efficiency is found to be 31.25 cm2/C for the as-deposited films and decreases to 18.3 cm2/C by annealing films at 723 K.