Influence of Er and Yb on photoelectrochemical performance of TiO2 thin film

Abstract

The strategy of modifying the titanium dioxide photoanode with an internal upconverter containing Er activator and Yb sensitizer was proposed. To assess the impact of rare earth ions, thin film TiO2, TiO2:Er, and TiO2:Er,Yb were deposited in the magnetron sputtering process on conducting glass, amorphous silica a-SiO2, and silicon. Two strategies were tested: introduction of high activator content and incorporation of low activator content with addition of sensitizer. Pure TiO2 served as a reference material. All deposited films displayed promising optical properties, such as high transparency and low reflectance in weak absorption region, and strong absorption above the fundamental absorption edge, as investigated by spectrophotometric measurements. Structural characterization by means of grazing incidence X-ray diffraction and transmission electron microscopy revealed that films crystallized as a mixture of anatase and rutile, while high concentration of modifying ions led to amorphization. Changes in surface morphology accompanied the structural transition, as shown in scanning electron microscopy analysis. Current-voltage and time-dependent measurements in photoelectrochemical cells, under white light illumination before and after cut-off of ultraviolet light, confirmed enhanced performance of TiO2:Er,Yb (1 at.%, 1 at.%) photoanodes over pure TiO2 as well as TiO2:Er (10 at.%) and TiO2:Er,Yb (2 at.%, 10 at.%).