Improved current collection in WO₃:Mo/WO₃ bilayer photoelectrodes

We report on the incorporation of molybdenum into tungsten oxide by co-sputtering and its effect on solar-powered photoelectrochemical (PEC) water splitting. Our study shows that Mo incorporation in the bulk of the film (WO₃:Mo) results in poor PEC performance when compared with pure WO₃, most likely due to defects that trap photo-generated charge carriers. However, when a WO₃:Mo/WO₃ bilayer electrode is used, a 20% increase of the photocurrent density at 1.6 V versus saturated calomel reference electrode is observed compared with pure WO₃. Morphological and microstructural analysis of the WO₃:Mo/WO₃ bilayer structure reveals that it is formed by coherent growth of the WO₃:Mo top layer on the WO₃ bottom layer. This effect allows an optimization of the electronic surface structure of the electrode while maintaining good crystallographic properties in the bulk.