Electrochromic Thin Films Based on NiAl Layered Double Hydroxide Nanoclusters for Smart Windows and Low-Power Displays

Abstract

To develop electrochromic thin films for smart windows and low-power displays, homogeneous thin films were produced by spin coating colloidal NiAl layered double hydroxide (LDH) nanocluster solutions on a fluorine-doped tin oxide (FTO) glass substrate. The nano-LDH dispersion was synthesized via a facile one-step epoxide mediated process at room temperature. In situ relative transmittance measurements at 400 nm, recorded during potential scans in cyclic voltammetry or differential pulse chronoamperometry, showed the electrochromic behavior of the homogeneous thin films. The impact of various parameters on the electrochromic properties of the films was detailed, such as the thickness of the film, the nature of the electrolyte, and the presence of electroactive anions. The electrochromic properties, namely, the change in transmittance (ΔT) and the bleaching reversibility, were greatly improved using alkaline metal hydroxide as the electrolyte and in the presence of Fe(CN)64–. The performances that we reached from the deposition of nanoclusters can be advantageously compared to the literature with ΔT = 70% and fast and good reversibility. Upon calcination, the NiAl-LDH film converted into mixed oxides (NiO and NiAl2O4). The higher the calcination temperature, the lower was the ΔT value. The presence of porosity within the thin films, through the introduction of sacrificial polymeric beads and then decomposition at 400 °C, was investigated, highlighting an enhancement of the ΔT value attributed to better accessibility to the nickel redox sites.