Cu-Doped and Un-Doped WO3 Photochromic Thin Films

In this work, 0%, 0.5%, 1%, and 2% Cu-doped WO3 nanoparticles were synthesized via a polyol method. The as-synthesized materials were characterized by x-ray diffraction, scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), x-ray photoelectron spectroscopy (XPS), and UV-Vis photochromic activity. A bond valence model was adopted to explain the relationship between the lattice parameter and Cu percentage. Additionally, two films (1% Cu-doped and un-doped samples) obtained by dip-coating from a well-dispersed suspension were optically investigated using ex situ and in situ UV-Vis spectrometry; coloring/bleaching kinetics were thoroughly studied. The Cu-doped WO3 film was found to have a high-quality bleaching mechanism (five times as fas as the un-doped WO3 film). Finally, the high bleaching performance of the doped films was confirmed by successive cycling, showing that the as-prepared compounds are of great interest for smart window applications, for example.