Effects of copper-doping on electrochromic properties of titanium dioxide films

Doping with metal elements is a valid way to alter the electrochromic performance of single materials. The doped metal ions can modify the electronic structure of the pristine materials, this results in a change in the transfer and migration of electrons or ions in electrochromic reactions. In this work, a series of copper (Cu)-doped titanium dioxide (TiO₂) films (0.5%, 1% and 5 wt%) were fabricated by a hydrothermal method and a subsequently spin-coated approach. The effects of doped Cu on the morphological structure, crystallinity, elemental chemical state and electrochromic properties of TiO₂ films were evaluated by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical techniques. The doping of Cu into TiO₂ exerts a substantial influence on its crystal structure, with a marked deterioration in crystallinity observed as the doping concentration increases. The results show that the ionic diffusion coefficient of the 0.5% Cu-TiO₂ film is 7.74 × 10⁻¹⁰ cm²/s, the light modulation range is as high as 50.3%, the bleaching and colouring switching times are 1.95 and 16.43 s, respectively, and the light transmittance retention rate can be maintained after 200 cycles. Overall exhibits preferred electrochromic and electrochemical properties. This study indicates that Cu doping with moderate concentration is a feasible way to heighten the electrochromic property of TiO₂.