Fast Switching of Photoelectrochromic Device Using Ligand Attached TiO2 Layer

Abstract

We fabricated a scalable and economical photoelectrochromic smart window that can be darkened under illumination and bleach in dark conditions. The materials used in this device can cut the cost by omitting transparent conducting oxide and ruthenium dye. The device is composed of a screen-printed WO3 layer on the soda-lime glass, a screen-printed TiO2 layer that is modified by attaching a ligand (5-methyl salicylic acid), a redox mediator and a soda-lime cover glass. The performance of the different types of salicylic acid ligands is investigated first in the dye-sensitized solar cells. The best performing ligand (5-methyl salicylic acid) was then used in the photoelectrochromic device. Using soda-lime glass and 5-methyl salicylic acid instead to conducting glass and ruthenium dye results in higher stability with additional benfit of low cost. The change in transmittance of the device also depends upon the thickness of WO3 and TiO2 layers and the optimized thickness was used in the device. The device showed fast coloring with a change in transmittance of 40% at 550nm within 3 minutes. However, the device showed slow bleaching and took 3 hours to bleach partially and 24 hours to bleach fully. To address the issue of slow bleaching, platinum particles were added in the WO3 and TiO2 layers to speed up the back reaction. The Pt particles used as a catalyst showed a dramatic improvement in the bleaching speed of photoelectrochromic device without affecting the coloring performance of the device. The device bleached fully within 30 minutes in the dark when Pt was incorporated in the WO3 layer.