A single-layer approach to electrochromic materials

Abstract

This study is focused on the development of electrochromic (EC) materials that could be incorporated into electrically-driven switchable devices such as electrochromogenic glasses. The ultimate goal of this research is to depart from the complexity of the EC device construction which is in use today. Such construction consists of three layers each of them incorporating a specific functionality: the electrochromophore, the electrolyte and the ion storage, assembled between two transparent or reflective electrodes. In most of these conventional devices the electrolyte layer is a liquid or a gel. Since solid-state EC devices are of high commercial interest, we are exploring various avenues to reduce the number of layers to one layer that is all-solid and electrochromically/electrolytically and ionically functional. The design strategy is based on the use of polymers such as poly(epichlorohydrin-co-ethylene oxide), poly(vinyl butyral) and poly(ethylene-co-methacrylic acid) ionomer, to which EC properties were introduced by grafting reactions with specifically synthesized carbazole derivatives. A combination of analytical techniques was used to characterize the monomers and the carbazole-grafted polymers. A proof of concept was demonstrated for a single-layer, all-solid-state EC device consisting of a film of poly(ECH-co-EO) containing pendent carbazole groups, assembled between two transparent electrodes, Sn-doped In 2 O 3 oxide-coated glasses.