Electrochemical modification of the optical and electrical properties of Cd-rich NixCd1-xO alloys

Enhancement of the optical and electrical properties of Cd-rich NixCd1−xO alloys was achieved through an electrochemical procedure - their biasing at a constant negative potential into an electrolyte. Depending on the conductivity of the film (correlated to x), the films changed their color from transparent-yellowish to black. For a certain bias, the coloration became permanent and irreversible. Electron concentration for some samples increased for better than two orders of magnitude upon the coloration, while as the mobility decreased for a factor of 2-10. Rutherford Back Scattering (RBS) analysis revealed oxygen deficiency for the colored samples. The XRD analysis showed that the coloration could be associated to a partial reduction of CdO2 to CdO. XPS analysis suggested complex red-ox transitions of the two Ni and two Cd-oxides within the alloy. Ni2p electrons suggested that a partial NiO (transparent) transition to Ni2O3 (black) is likely the responsible process for the occurrence of the intensive light trapping. Since the NixCd1−xO band gap is tunable with x, one may conclude that this electrochemical procedure is motivating for tuning/modification/enhancement of the both, the absorption and conductivity of NixCd1−xO films for their possible application as integrated film photoanodes (TCO and PEC cell in one) within a hybrid water splitting device.