A fast-switching light-writable and electric-erasable negative photoelectrochromic cell based on Prussian blue films

We report a fast-switching negative photoelectrochromic cell composed of a dye-sensitized nanocrystalline TiO2 electrode and Prussian blue counter electrode sandwiching a LiI electrolyte. The cell can be bleached under illumination with shorted TiO2 and Prussian blue electrodes, and re-colored by applying an appropriate external voltage. The photo-bleaching and electric-coloring processes are fast and reversible. A maximum absorbance modulation of 0.44 recorded at 700 nm is obtained between bleached and colored states for the cell when the PB filmʹs thickness is 452 nm. Illuminated under different levels of light intensity or durations of time, the shorted cell shows adjustable optical absorption from 470 to 840 nm. The in-situ transmittance response depicts that the photo-bleaching response is 6.2 s for 70% transmittance change under 100 mW/cm2 illumination in short circuit configuration, and the re-coloration time is about 600 ms under 2 V bias recorded at 780 nm, with an electrochromic coloration efficiency of 103.4 cm2/C. The cell shows a good reversible stability and can be potentially applied in erasable displays.