Origin of the Memory Effect in Electrochromic Sputtered WO<sub>3</sub> Films: Composition, Structure, or Morphology?
Brandon Faceira, Lionel Teulé‐Gay, Jade Le Hébel, Christine Labrugère‐Sarroste, Fabienne Ibalot, Hou‐Yi Huang, Yucheng Huang, Chung‐Li Dong, Jean‐Paul Salvetat, Mario Maglione, Aline Rougier
Abstract
Abstract The memory effect property, described as a reversible color persistence while the potential is withdrawn, is of particular importance to reaching zero‐energy consumption electrochromic devices. Nevertheless, often observed in organic materials, it is poorly studied in oxides. In this study, electrochromic tungsten oxide thin films are elaborated at different working pressures by radiofrequency magnetron sputtering. The influence of the deposition pressure on the electrochemical properties of WO 3 films as well as on their memory effect is investigated. Three kinds of WO 3 films can be distinguished: with irreversible blue coloration, with reversible coloration presenting a high memory effect, and with reversible coloration with a low memory effect. The origin of these discrepancies is studied through the composition, the local atomic environment, and the morphology of the WO 3 thin films. An increase of transmittance at 550 nm as low as 15.8% in 48 h in air and 5.2% in 24 h in the electrolyte is recorded. This study highlights a better understanding of the memory effect property of electrochromic oxides for low‐consumption energy electrochromic devices, pointing out morphology as a key parameter.