Optical Sensing by Silica/Titania Thin Films Doped with Oxacarbocyanine Dye

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO₂/TiO₂ matrix structures depending on the Si : Ti ratio.