(Invited) Observing Photochemical Charge Transport at Particle Based Tandem Junctions for Overall Water Splitting

Abstract

Photochemical charge generation, separation, and transport across particle interfaces are central to photoelectrochemical water splitting, a pathway to hydrogen from solar energy. Here we use surface photovoltage spectroscopy (SPS) to probe these processes in films of BiVO4 and Rh:SrTiO3 particles on fluorine doped tin oxide (FTO) or p-doped silicon wafers. Particle films were made by drop-coating of premade particle suspensions in water followed by thermal annealing. Photochemical charge separation in the films was measured as a function of layer thickness and illumination intensity, and in the presence of sacrificial electron donors. The formation of Tandem junctions is clearly observed and to result in a maximum photovoltage of up to -150 mV under 0.3 mW cm-2 illumination. Charge separation is limited by light absorption and by slow electron transport. Overall Water Splitting with visible light an a quantum efficiency of 0.61% at 400 nm was observed with a direct contract tandem photocatalysts made of ruthenium-loaded Rh:SrTiO3 nanocrystals and of BiVO4 microcrystals. The activity and stability of this system depends on the temperature employed for generating the tandem junction. The ability to measure the built-in potential in particle junctions promotes the development of particle-based systems for artificial photosynthesis. Figure 1