Solution-processed multilayered BiVO4 photoanodes: influence of intermediate heat treatments on the photoactivity

Spin coating of successive layers is a convenient method for fabricating metal oxide photoelectrodes with tunable thickness from a precursor solution. In this study, the crystallization behavior and photoelectrochemical properties of spin-coated BiVO4 films are investigated as a function of the brief heat treatments applied after depositing each individual layer. We find that full crystallization of the final films can only be obtained when the films are subjected to 10 min intermediate heat treatments to at least 350 degrees C. Heat treatments at lower temperatures result in films which remain partially amorphous, even after final treatment at 460 degrees C. For intermediate heat treatments above 350 degrees C the layers fully crystallize to the desired monoclinic scheelite phase, showing improved carrier separation efficiencies but lower efficiencies for charge injection into the electrolyte. These findings suggest that choosing the right processing conditions is an essential first step towards improving the performance of solution-processed BiVO4 photoelectrodes.