Synthesis, characterization and dual-band electrochromic properties of Nb-doped WO3 films

Nb-doped WO 3 films were prepared on FTO substrates by a facile sol–gel dip coating method. The influence of Nb doping on the microstructure and electrochromic characteristics of the films have been   explored. The results indicate that the pure WO 3 film can achieve a synchronizing modulation of visible and near-infrared light bands by suppling voltage. However, the Nb-doped WO 3 films exhibit an ability of independent and selective transmittance modulation in both bands. Moreover, the Nb-doped WO 3 films undergo two electrochromic processes at different voltages, which are local surface plasmon resonance (LSPR) electrochromic process and electrochemical redox electrochromic process, respectively. These two electrochromic processes exhibit a unique photoelectric conversion behavior, that is, the reversible “bleached and warm” - “bleached and cool” - “colored and cool” modes. Additionally, with the increase of Nb doping content, the LSPR electrochromic effect becomes stronger. The high LSPR enhances the electrochemical redox electrochromic performance of the Nb-doped WO 3 films, enabling them to exhibit better electrochromic performance in the visible and near-infrared bands.