Electrodeposition-based electrochromic devices with reversible three-state optical transformation by using titanium dioxide nanoparticle modified FTO electrode

Reversible electrodeposition-based electrochromic devices are highly promising for extensive applications owing to their facile and low-cost fabrication. Herein, a novel electrodeposition-based electrochromic device with reversible three-state optical transformation, i.e. transparent, mirror, and black, was fabricated by introducing a fluorine-doped tin oxide (FTO) electrode modified with commonly available and inexpensive titanium dioxide (TiO2) nanoparticles. Typically, the fabricating strategy mainly involved three procedures, namely obtaining a stable dispersion of TiO2 nanoparticles by milling, achieving a surface modification of the FTO electrode with TiO2 nanoparticles by spin-coating and sintering, and assembling the device by sandwiching gel electrolyte between the modified FTO electrode and a flat FTO electrode. By applying different voltages for a short while, this transparent smart device can be immediately switched to black (+2.5 V/20 s) or mirror (-2.5 V/20 s) state by depositing Ag on the surface of the modified or unmodified FTO electrode respectively. There is below 1% transmittance in the black state and over 80% reflectance in the mirror state for the device. By changing the surface structure of the TiO2 modified FTO electrode, the optical properties of the device in different states can be controlled effectively. Moreover, the optical transformation exhibited good stability over 1500 cycles of testing.