Effect of annealing temperature on photogenerated charge transfer in electrochemically-synthesized nanostructured tungsten trioxide thin films

Background: Various nanostructured thin films on photoelectrodes have been utilised in photoelectrochemical (PEC) water splitting process for solar hydrogen fuel conversion. However, the overall solar conversion efficiency is still relatively low and this could be due to the rapid recombination of photogenerated charge carriers at molecular level. Objective: The main aim of this paper was to understand the effect of annealing temperature on the photogenerated charge transfer in nanostructured tungsten trioxide (WO3) thin films synthesized via electrochemical deposition route. Results: Amorphous WO3 films were annealed between 100oC and 600oC. It was found using electrochemical impedance spectroscopy (EIS) that both the charge-transfer and transport resistances decrease with increasing annealing temperature. Conclusion: This study concluded that a properly controlled annealing treatment is crucial in regulating the nanocrystals growth, which subsequently enhances the photogenerated charge transfer and solar conversion efficiency for sustainable hydrogen production from water splitting.