Sol-gel chromogenic materials and devices

Abstract

In the last few years the sol-gel process has turned into an interesting and promising method of synthesizing materials for obtaining thin or thick films with definite functions. The techniques of film preparation such as dip and spin coating are simple and allow us to prepare coatings with smooth optical surfaces with controlled stoichiometry, structure and texture. In this paper we give an up to date overview of what has been achieved in the field of chromogenic materials such as anodic or cathodic electrochromic coatings, counter or ion storage electrodes, transparent electron conductors and ionic conductors to be used in electrochromic (EC) devices. We also review the sol-gel research in the related areas of photochromic, thermochromic and electrooptic sol-gel materials whose properties are essentially used to modulate the luminous or solar energy as well as sol-gel materials prepared in the form of nanopartieles proposed recently for the development of a new type of solar cell. Finally we stress the future developments in these fast growing fields.

Electrochromic and electrochemical capacitive properties of tungsten oxide and its polyaniline nanocomposite films obtained by chemical bath deposition method

“…One of such is that by Schirmer et al [8], in which they proposed that the optical absorption of the films is caused by the small polaron (SP), or transitions between two non-equivalent sites of tungsten ( 3 ) during coloration and an electron and cation deintercalation reaction during bleaching [7,9] according to the following equation: Conducting polymeric materials like polypyrrole (PPy), Polyaniline (PANI) and polythiopheres etc. have been considered as EC materials but among these, PANI has emerged as the most promising active materials for electrochromic devices due to its high capacitive characteristics, relative ease in preparation, good environmental stability and tuneable conductivity [10].…”

“…The main challenge is managing to synthesize inorganic-organic hybrid combinations that keep or enhance the best properties of each of the components while eliminating or reducing their particular limitations. Tungsten oxide shows electroactivities over comparatively negative potential range and is a cathodic EC material which changes color from transparent or yellow to deep blue with large optical modulation when it is reduced by H + or Li + while PANI is an anodic coloration material [9,30]. Nano-composite film of WO 3 / PANI tends to enhance the properties of the two materials singly while reducing their shortcomings.…”

Optical and kinetic properties of cathodically deposited amorphous tungsten oxide films

“…The coloration and decoloration processes in the near infrared and visible regions of optical spectrum are effected by double ionelectron injection and extraction [1][2][3][4]. The coloration of an a-WO 3 electrode in the course of current flow is caused by the capture of electrons injected into the film onto the unoccupied d-orbitals of W 6+ centers with their reduction to W 5+ centers (with the change of the tungsten oxidation state from +6 to +5), which are just a-WO 3 color centers.…”

“…Amorphous tungsten oxide (a-WO 3 ) films find application in electrochromic devices [1][2][3]. The coloration and decoloration processes in the near infrared and visible regions of optical spectrum are effected by double ionelectron injection and extraction [1][2][3][4].…”

Fe-containing CeVO4 films as Li intercalation transparent counter-electrodes

“…WO 3 is one of the most extensively investigated EC material giving the best EC performance due to its high charge capacity and long-term cyclability [1]. Less work has been devoted to the development of the appropriate counter-electrodes although many transition metal oxides have been proposed to work in tandem with WO 3 in EC devices [2]. However, only those materials with a photopic transmittance above 70% in the intercalated state, a charge capacity comparable to WO 3 coupled to a high stability and reversibility with long-term cycling can be considered as promising optically passive counter-electrodes [3].…”