Flexible nano-photo-electrochromic film

A flexible nano-photo-electrochromic poly(ethylene terephthalate) (PET)-TiO2-PO4-methylene blue (MB) based film was obtained by the deposition of TiO2 nanoparticles on a PET conductive substrate. A further covalent chemical bond of MB molecules on the TiO2 film by means of phosphate groups ensures the photo-electrochromic properties of this device. Indeed, MB molecules can change color both owing to the irradiation with red light, in the presence of electron donor molecules, and owing to the oxidation reaction with an oxidizing agent. Because the oxidation reaction of MB molecules occurs at the same electrode where the molecules are anchored, the film shows a very fast coloration time (600 ms). The thermal stability of the film and the anchoring of MB molecules on TiO2 nanoparticles were investigated by the differential scanning calorimetry technique. The morphologies of the surface and cross section of the TiO2 layer were studied by a scanning electron microscope. Moreover, the device was characterized in terms of light absorption by UV-visible spectroscopy and optical transmission by an optical line.