Unprecedented Electrochromic Stability of a-WO_3–x Thin Films Achieved by Using a Hybrid-Cationic Electrolyte

Abstract

With large interstitial space volumes and fast ion diffusion pathways, amorphous metal oxides as cathodic intercalation materials for electrochromic devices have attracted attention. However, these incompact thin films normally suffer from two inevitable imperfections: self-deintercalation of guest ions and poor stability of the structure, which constitute a big obstacle toward the development of high-stable commercial applications. Here, we present a low-cost, eco-friendly hybrid cation 1,2-PG-AlCl3·6H2O electrolyte, in which the sputter-deposited a-WO3–x thin film can exhibit both the long-desired excellent open-circuit memory (>100 h, with zero optical loss) and super-long cycling lifetime (∼20,000 cycles, with 80% optical modulation), benefiting from the formation of unique Al-hydroxide-based solid electrolyte interphase during electrochromic operations. In addition, the optical absorption behaviors in a-WO3–x caused by host–guest interactions were elaborated. We demonstrated that the intervalence transfers are primarily via the “corner-sharing” related path (W5+ ↔ W6+) but not the “edge-sharing” related paths (W4+ ↔ W6+ and/or W4+ ↔ W5+), and the small polaron/electron transfers taking place at the W–O bond-breaking positions are not allowed. Our findings might provide in-depth insights into the nature of electrochromism and provide a significant step in the realization of more stable, more excellent electrochromic applications based on amorphous metal oxides.

MOF‐Derived Carbon Embedded NiO for an Alkaline Zn−NiO Electrochromic Battery

“…Interestingly here bleaching times for the films are relatively longer compared to the coloration times. Two possible statements are there to explain this phenomenon – (a) while ion intercalation takes place, the possible lattice deformation try to obstruct the movements of incoming ions, but the presence of carbon in the material try to hasten the process up to a certain level, and (b) during deintercalation of ions, the built‐in electric field at the interface works in opposite direction of the ionic movement, resulting the longer bleaching time [51] …”

“…Two possible statements are there to explain this phenomenon -(a) while ion intercalation takes place, the possible lattice deformation try to obstruct the movements of incoming ions, but the presence of carbon in the material try to hasten the process up to a certain level, and (b) during deintercalation of ions, the built-in electric field at the interface works in opposite direction of the ionic movement, resulting the longer bleaching time. [51] Coloration efficiency (CE) is yet another important analytical parameter for electrochromic materials which tells us about the requirement of power during electrochromic switching. It is defined as the ratio of change in optical density (ΔOD) and injected/extracted charge density per unit area (mC/cm 2 ).…”

Photonic Drying/Annealing: Effect of Oven/Visible Light/Infrared Light/Flash-Lamp Drying/Annealing on WO3 for Electrochromic Smart Windows

“…However, the pristine sample (without drying) was not good for ECDs due to its amorphous character with weak (002), (200), and (202) diffraction peaks. The pristine sample was unsuitable for application in ECDs because of its low chemical stability. , Besides, the WO 3 films dried/annealed by different techniques like visible light/IR light/flash-lamp/oven show good optical modulation owing to the insertion of ions from the electrolyte in the WO 3 lattice, resulting in charge neutrality of the entire area of ECD. Also, no significant difference was observed in the diffraction peaks of WO 3 , which may be due to the possible chemisorption of oxygen on the W surface or the evaporation of adsorbed water molecules.…”

Determination of W(V) in WO3 Photochromism Using Localized Surface Plasmon Resonance of Ag Nanoparticles

“…The blue coloration occurs because of the absorption from the red region of the visible light to the near-infrared region. Among them, WO 3 is the most studied material due to the electrochemical reversibility and stability for a practical application such as smart windows, which control solar radiation transmitted through the windows. − Many efforts have been made to enhance the electrochromic performance by combining with conducting materials such as graphene and conductive polymers. , An important factor in estimating the electrochromic performance is the coloration efficiency, i.e., the change in optical density divided by charge density which is consumed per unit electrode area . High coloration efficiency means a large optical modulation range with small charge intercalation or extraction.…”