Influence of organic additive on the morphological, electrical and electrochromic properties of sol-gel derived WO3 coatings

The WO3 electrode is ubiquitous in an electrochromic device (ECD) and is a common choice as the electrochromic (EC) layer. EC films were deposited on different substrates by spin coating using peroxotungstic acid based precursor solutions followed by appropriate thermal treatment. Many properties of the films, including some of the EC properties dependant on microstructure of the films, were found to be modified by the addition of small amounts of organic acid to the precursor solution. A study of structural, electrical and electrochromic properties of films cast by using precursor solution comprising 0 to 10 wt% of oxalic acid dihydrate (OAD) was carried out in terms of surface morphology, electrical resistance, structure and EC response. The important findings are that the addition of oxalic acid to the precursor solution results in films with excellent EC properties, devoid of cracks and decreases their dc electrical resistance.