A thorough study on electrochromic properties of metal doped tungsten trioxide film prepared by a facile solution process

In this research, we investigate the effect of metal doping on the electrochromic (EC) performance of tungsten trioxide (WO3) films. These films were prepared by a novel method involving solution processing and thermal annealing. In this procedure, ammonium tetrathiotungstate ((NH4)2WS4) was dissolved in dimethylformamide at a high concentration ratio (200 mg mL−1) to obtain a homogeneous solution and then spin-coated onto the indium thin oxide (ITO) substrate for use as a working electrode. Subsequently, the film was annealed at the different temperatures (200, 300, 400, and 500 °C) to form a crystal structure of WO3. X-ray diffraction, Raman, and X-ray photoelectron spectroscopic results confirm the crystal formation of WO3. Moreover, in order to improve the electrochromic performance, different concentrations (10, 20, 30, and 40 mM) of different metal chlorides such as PtCl4, PdCl2, AuCl3, AgCl, CuCl2, NiCl2, NaCl, and KCl were added into the (NH4)2WS4 precursor and the mixture was coated on the ITO substrate and annealed at 500 °C. The results indicate that the performance of the Au-doped WO3 film was better than those with other dopants, likely as a result of the plasmonic effect. Therefore, the proposed method and Au-doped WO3 films are great candidates for the development of smart windows with high EC performance.