Influence of ITO electrode on the electrochromic performance outcomes of viologen-functionalized polyhedral oligomeric silsesquioxanes

Abstract

Electrochromic devices (ECDs) exhibit reversible optical changes under applied electrical stimuli. Transparent conducting electrodes (TCOs), generally constructed with indium tin oxide (ITO), are a vital component determining transparency and switching behaviors. ITO specifications for TCO materials have not drawn much attention despite the critical role of these materials. Herein we investigate the influence of ITO electrodes in achieving high-performance ECDs containing viologen-functionalized polyhedral oligomeric silsesquioxane (POSS-viologen). Indeed, ITO electrodes exert significant effects on the electrochromic characteristics. A high ITO thickness shows superior color-switching with high optical density and coloration efficiency levels. Enhanced electrical conductivity facilitates diffusion behaviors, an outcome beneficial for electrochromic switching. The surface-charge capacity ratio values are measured and found to be close to one, indicating that no residual current remains, and the prepared devices provide good reversibility during the coloring and bleaching process. Furthermore, with an increase in the ITO thickness, the current required for the coloring and bleaching processes decreases, and the power consumption needed for the operation of the device becomes low. The superiority of POSS-viologen should also be noted, especially when compared to normal viologens, in terms of the electrochromic properties and long-term operational stability. These results demonstrate the critical role of electrical conductivity in ITO electrodes, providing a valuable guideline for TCO specifications for ECD fabrication using viologen derivatives.