Preparation and photoelectrochemical properties of Ti1−xVxO2 solid solution thin film photoelectrodes with gradient bandgap

A design of a gradient bandgap Ti_1?xV_xO₂ thin film electrode for wet-type solar cells is provided. The gradient bandgap film electrodes were prepared by heating stacked layers of varying V/Ti ratios using the sol-gel method. A composition gradient was observed for some of the samples by X-ray photoelectron spectroscopy although it was not very large. For the Ti_1?xV_xO₂ film electrodes, conspicuous visible light photoresponse and photoelectrochemical stability were observed. The photocurrent increased with increasing bias potential. However, the photocurrent onset potentials of the Ti_1?xV_xO₂ film electrodes were more positive than those of TiO₂ film electrodes, probably owing to the high surface state density introduced by the diffusion of vanadium ions.