(Invited) Using Surface Photovoltage Spectroscopy to Observe Photovoltage Generation at the Interfaces of Cu2o, BiVO4, and Rh:SrTiO3 Particles

Abstract

Surface photovoltage spectroscopy (SPS) allows contact-less measurement of the Galvani photopotential at the interfaces of particles under illumination. Here we use SPS to observe the light intensity and wavelength dependent photopotential in a Ru–SrTiO3:Rh/BiVO4 particle tandem overall water splitting photocatalyst and in particle layers made of Cu2O and BiVO4. For the tandem, a photovoltage develops above 2.20 eV, the effective band gap of the tandem, and reaches its maximal value of −2.45 V at 435 nm (2.44 mW cm–2), which corresponds to 96% of the theoretical limit of the photocatalyst film on the fluorine-doped tin-oxide-coated glass (FTO) substrate. Charge separation is 82% reversible with 18% of charge carriers being trapped in defect states. The unusually strong light intensity dependence of the photovoltage (1.16 V per decade) is attributed to depletion layer changes inside of the BiVO4 microcrystals. Isolated Cu2O particle layers on FTO show p-type behavior and BiVO4 particles show n-type behavior. In a FTO/Cu2O/BiVO4 particle stack, both particles act in tandem, producing up to -2.1 V photovoltage under 2.5 eV excitation, which corresponds to 90% of the ideal limit. The photovoltage spectra also reveal the effects of shading at high excitation energy and the effects of low absorber strength at low excitation energy. These results are relevant to the understanding of photochemical charge transfer at irregular particle surfaces and to the construction of devices for artificial photosynthesis and water splitting. Figure 1