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

By Ristova, Mimoza M.; Francis, Christopher; Toma, Francesca M.; Yu, Kin M.; Walukiewicz, Wladislaw
Published in Solar Energy Materials and Solar Cells NULL 2016

Abstract

Abstract 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.

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