Photoelectrochemical Investigation and Electronic Structure of a p-Type CuNbO3 Photocathode

A new p-type CuNbO3 photoelectrode was prepared on fluorine-doped tin oxide (FTO) glass and characterized by X-ray diffraction (XRD), UV–vis spectroscopy, and photoelectrochemical techniques. Solid-state syntheses yielded a red-colored CuNbO3 phase (space group: C2/m (No. 12), Z = 8, a = 9.525(1) Å, b = 8.459(2) Å, c = 6.793(1) Å, β = 90.9(2)°) with a measured optical bandgap size of ∼2.0 eV. Phase-pure samples could be deposited and annealed on FTO slides at 400 °C under vacuum. Photoelectrochemical measurements showed the onset of a photocathodic current driven under visible-light irradiation and reaching incident-photon-to-current efficiencies exceeding ∼5%. The p-type CuNbO3 film also exhibits a stable photocurrent and notable resistance to photocorrosion, as shown by X-ray diffraction. Electronic structure calculations based on density functional theory reveal the visible-light absorption originates from a nearly direct bandgap transition owing primarily to copper-to-niobium (d10-to-d0) excitations. A promising new p-type semiconductor is thus revealed of potentially broad use in solar-energy conversion.