Cadmium Ferrocyanide Overlayers: Regulation of Photoinduced Charge Transfer at the N-cdse/[Fe(CN)⁶]⁴-^/3- Interface

Utilization of an n-CdSe photoanode in an electrolyte containing the ferro/ferricyanide redox couple (adjusted to pH =13) gives rise to an overlayer on the electrode composed of [Cd(CN)Fe(CN)⁶]²~^/1_. This layer is found to be effective with respect to supression of electrode photodecomposition processes. Enhanced interfacial charge-transfer rates are observed which give rise to excellent monochromatic (488 or 633 nm) cell output parameters for light intensities up to 400 mW/cm². Monochromatic maximum optical to electrical energy conversion efficiencies of 20% derive from fill factors typically in excess of 0.7 and limiting quantum yields for electron flow >0.6. This provides for limiting photocurrents as high as 100 mA/cm² under ideal conditions. The electrode response is found to be very sensitive to the nature of the etchant pretreatment employed and the spectator cations present in the supporting electrolyte. These parameters are found to affect the amount and microstructure associated with the interfacial overlayer. A novel wavelength dependence of the electrode stability is associated with photoaquation processes in the cyanometalate overlayer which modulates overlayer charge-transport properties.