Charge Dynamics as Probed by Small Signal-Modulated Photocurrent and Impedance Spectroscopy of Metal Vanadate Semiconductors and Alloys.

This study presents the combined and complementary use of two techniques, namely, intensity modulated photocurrent spectroscopy (IMPS) and photoelectrochemical impedance spectroscopy (PEIS) for the study of partially or wholly replacing copper with an alkaline earth metal (Mg, Ca) in a metavanadate compound matrix (MV2O6). To this end, the three reference compounds (CuV2O6, CaV2O6, MgV2O) and two alloy compositions (Mg0.1Cu0.9V2O6 and Ca0.1Cu0.9V2O6), obtained from a solution combustion technique, were screen-printed on fluorine-doped tin oxide glass (FTO) substrates. Wavelength discrimination for optical excitation of these semiconductor samples was provided by using high-power LED (front-side) illumination with different wavelengths, UV (λ = 370 nm), blue (λ = 455 nm), green (λ = 535 nm), and red (λ = 670 nm). A nonunity photogeneration yield of mobile charge carriers was seen in a trend reminiscent of previous data on binary oxides or even for other types of ternary copper oxides from other laboratories. The dynamic aspects of charge transfer and carrier recombination are discussed using the combined IMPS-PEIS data along with other optical (e.g., diffuse reflectance spectroscopy) and photoelectrochemical data.