Wavelength-Dependent Ultrafast Charge Carrier Separation in the WO₃/BiVO₄ Coupled System

High Resolution Image Download MS PowerPoint Slide Due to its ∼2.4 eV band gap, BiVO 4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO 3 /BiVO 4 heterojunction films, the electrons photoexcited in BiVO 4 are injected into WO 3, overcoming the lower charge carriers’ diffusion properties limiting the PEC performance of BiVO 4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO 4 excitation, a favorable electron transfer from photoexcited BiVO 4 to WO 3 occurs immediately after excitation and leads to an increase of the trapped holes’ lifetime in BiVO 4 . However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO 4 . PEC measurements reveal the implication of these wavelength-dependent ultrafast interactions on the performances of the WO 3 /BiVO 4 heterojunction.