Gradient Carrier Doping as a Method for Maximizing the Photon-to-Current Efficiency of a SrTiO3 Water-Splitting Photoanode

Photoelectrochemical solar water splitting is a potentially useful way to store solar energy in a renewable fuel in the form of hydrogen. For practical use of an efficient and reliable system, a quantitative understanding of the operational mechanism is required to clarify the influence of each physical and chemical parameter on the photoelectrochemical function. In this study, we investigate the effect of carrier density on the photoelectrochemical activity of a SrTiO3 photoanode by using well-defined SrTiO3 single crystals. A clear trade-off relationship as a function of carrier density is revealed. Based on the understanding of carrier density dependence, we propose a method of gradient carrier doping as a rational way to maximize the photon-to-current efficiency of a photoelectrode. By grading the carrier density in the depth direction, the designed SrTiO3 photoanode showed close to 100% incident photon-to-current efficiency at a wavelength of 300 nm.