The significant effect of heterojunction quality on photoelectrochemical water splitting in bilayer photoelectrodes: Rb(x)WO3 thin films on RbLaNb2O7 layers.

We have prepared nearly perfect hexagonal m-plane-oriented RbxWO3 films on (010)-oriented RbLaNb2O7 layers. The prepared bilayer films showed Rb diffusion from the RbLaNb2O7 seed layers, and we obtained uniaxially oriented RbxWO3/Rb1-yLaNb2O7 photoanodes. The RbxWO3/Rb1-yLaNb2O7 bilayer photoanodes exhibited enhanced photoelectrochemical water splitting compared with the RbxWO3 and RbLaNb2O7 monolayer photoanodes. Furthermore, we clearly demonstrated that the high crystal quality of the heterojunction significantly enhanced water splitting. The photocurrent density of the nearly perfectly oriented RbxWO3/Rb1-yLaNb2O7 photoanode that we prepared was 9.4-fold that of an unoriented bilayer photoanode. This increase was attributed to the inhibition of photo-excited charge recombination and stimulated electron transfer derived from low grain-boundary resistance.