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.