Electrochemical intercalation of O²⁻ in CuAlO₂ single crystal and photoelectrochemical properties

Abstract

The delafossite CuAlO₂ single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10⁻⁵ cm⁻² V⁻¹ s⁻¹. The chronoamperometry showed an electrochemical O²⁻ insertion with a diffusion coefficient D _303K of 3.3 × 10⁻¹⁸ cm² s⁻¹. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol⁻¹. CuAlO₂ is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and a holes density (N _A) of 10¹⁶ cm⁻³. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration depth (12 µm).