Enhanced Electrochromic Performances of Polyhedral Oligomeric Silsesquioxane (POSS) Modified Viologen Derivatives

Abstract

Polyhedral oligomeric silsesquioxane (POSS) is an inorganic silica nanocage surrounded by organic functional groups. Due to the presence of organic peripheries around the rigid case, functionalized POSS has often exhibited outstanding properties, thus finding useful for constructing porous inorganic-organic hybrid networks.The electrochromic devices (ECDs) offer noticeable color changes due to the electron transfer and redox reaction. The electrochromic materials play a critical role in determining the optical response and absorption intensity of the ECDs. Various electrochromic materials have been investigated, including inorganic metal oxides, viologens, and conducting polymers. Among these, viologen derivatives have been studied in depth owing to high electron-accepting capability and facile synthetic routes. Besides, viologen based ECDs have found various applications, such as smart windows, electronic paper, and the famous antiglare rearview mirrors developed by Gentex. However, critical weaknesses of viologens include low coloration efficiency, slow switching speed, and reduced long-term stability. Furthermore, the durability in the repeated operation of ECDs is limited in non-complementary device structures.Herein, we present the modification of viologen derivatives with the incorporation of POSS, in which the structural rigidity of POSS fillers and the synthetic versatility of viologen compounds are combined to ensure improved electrochromic performances. The solid-state ECDs are fabricated by sandwiching the single-layered ion gel containing POSS-modified viologens between two transparent electrodes. The resulting electrochromic behaviors are compared with those of conventional viologens, in terms of cyclic voltammetry, spectroelectrochemistry, and kinetic stability. Furthermore, the preparation of flexible ECDs using silver nanowire-PEDOT:PSS composite electrode is presented, and stable electrochromic operation in the repeated redox transitions is demonstrated on various plastic substrates.