Micro-Raman spectroscopy on polyethylene-glycol assisted sol–gel meso and macroporous WO3 thin films for electrochromic applications

Tungsten oxide (WO3) is one of the most promising materials for electrochromic devices and is currently investigated for applications in catalysis, ferroelectricity and in sensor technology. Here a molecular assembly approach to synthesize by sol–gel meso and macroporous thin films of tungsten oxide using polyethylene-glycol as a templating agent is reported. Micro-Raman spectroscopy has been employed to investigate the structure of WO3 thin films, deposited by dip-coating on glass, as a function of thermal annealing. This modified sol–gel route promotes the coexistence of a sub-stoichiometric monoclinic phase (most probably the WO2.72 phase) together with some hydrous phases (WO3·nH2O) even in samples heat treated up to 500 °C.