Abstract
The effects of compositionally induced changes on the semiconducting properties, optical response, chemical stability, and overall performance of KTaO3 photo-anodes in photoelectrochemical cells have been investigated. Single crystals of n-type Ca- and Ba-doped KTaO3 with carrier concentrations ranging from 0.45 - 11.5 x 1019 cm-3 were grown and characterized as photoanodes for hydrogen production in basic aqueous electrolytes. The photoelectrochemical properties of the crystals, including the photocurrent, photovoltage, and flat-band potential in contact with 8.5 M NaOH(aq) were relatively independent of whether Ca or Ba was used to produce the semiconducting form of KTaO3. All of the Ca- or Ba- doped KTaO3 single crystal photoanodes were chemically stable in the electrolyte; and based on the open-circuit potential and the band-edge positions, they were capable of unassisted photochemical H2 and O2 evolution from H2O. The minority carrier diffusion lengths values were small and comparable to the depletion region width. Photoanodic currents were only observed for photo-anode illumination with light above the band gap (i.e., �� < 340 nm). The maximum external quantum yield occurred at ��= ������ �� 1 nm (4.85 eV), and the depletion width plus the minority carrier diffusion length ranged from 20 to 65 nm for the various KTaO3-based photoanode materials.