New photoelectrochromic device

Abstract

A new photoelectrochromic device with excellent coloring and bleaching characteristics was developed. In contrast to other photoelectrochromic devices, the electrochromic layer (e.g. WO 3) and the photoactive layer (e.g. dye-covered TiO 2) are situated on the same TCO-coated glass substrate (TCO: transparent conductive oxide). The opposing electrode is a platinized TCO-coated glass. The electrolyte contains Li + and a redox couple (I − and I 3 −) in an organic solvent (e.g. propylene carbonate). Under illumination, the electrochromic layer is colored, and in the dark it is bleached. The advantage of this new device is that a catalyst (Pt) can accelerate the bleaching process independently of the coloration process. Thus a deep and fast coloration, and fast bleaching, can be achieved in the same device. The coloration is fast even for large areas, because the TCO is not necessary for the coloration process. Under 1 sun of illumination, we measured a transmittance change from 64 to 23% in 2 min. The bleaching time is about 2 min.