Highly efficient photocatalytic conversion of solar energy to hydrogen by WO₃/BiVO₄ core–shell heterojunction nanorods

Photocatalytic splitting of water under solar light has proved itself to be a promising approach toward the utilization of solar energy and the generation of environmentally friendly fuel in a form of hydrogen. In this work, we demonstrate highly efficient solar-to-hydrogen conversion efficiency of 7.7% by photovoltaic–photoelectrochemical (PV–PEC) device based on hybrid MAPbI₃ perovskite PV cell and WO₃/BiVO₄ core–shell nanorods PEC cell tandem that utilizes spectral splitting approach. Although BiVO₄ is characterized by intrinsically high recombination rate of photogenerated carriers, this is not an issue for WO₃/BiVO₄ core–shell nanorods, where highly conductive WO₃ cores are combined with extremely thin absorber BiVO₄ shell layer. Since the BiVO₄ layer is thinner than the characteristic carrier diffusion length, the photogenerated charge carriers are separated at the WO₃/BiVO₄ heterojunction before their recombination. Also, such architecture provides sufficient optical thickness even for extremely thin BiVO₄ layer due to efficient light trapping in the core–shell WO₃/BiVO₄ nanorods with high aspect ratio. We also demonstrate that the concept of fill factor can be used to compare I–V characteristics of different photoanodes regarding their optimization for PV/PEC tandem devices.