Study of WO3 films with textured surfaces for improved electrochromic performance

We present a study of electrochromic (EC) devices based on WO3 thin films w ith textured surfaces. Surface patterns were generated by electron gun depo sition of WO3 stripes (173-mum wide and 150-nm high) on a previously grown 'flat' WO, film, 150-nm thick. The films were characterized by SEM, XPS and FTIR. They are amorphous and near-sloichiometric and have a packing densit y of 0.8. The textured films were used for the fabrication of EC devices of the configuration: K-glass/WO3/1 M LiClO4 in PC/K-glass. These devices wer e characterized by optical and electrochemical techniques such as transmiss ion spectroscopy, cyclic voltammetry and GITT. They exhibit considerable re duction of transmittance in the visible with the application of a potential of 4 V for 30 s, stability and reversibility of their electrochromic prope rties with an open-circuit memory of more than a week. Compared to equivale nt EC devices with 'flat' WO3 films, the textured ones exhibit nearly doubl e diffusion coefficient for Li+ and up to 30% more current during cyclic vo ltammetry tests. Hence, they present a significant improvement over 'flat' films, due to better access of Li ions into the WO3 matrix. The textured WO 3 films are suitable for EC applications as they exhibit sharp contrast bet ween regions with different shades of blue in the colored state. Other. mor e complicated texture patterns are possible. (C) 2001 Elsevier Science B.V. All rights reserved.