Photovoltaic performance improvement of dye-sensitized solar cells based on tantalum-doped TiO2 thin films

Dye-sensitized solar cells based on a tantalum (Ta)-doped TiO2 thin film prepared by the hydrothermal method show a photovoltaic efficiency of 8.18%, which is higher than that of the undoped TiO2 thin film (7.40%). The Mott-Schottky plot indicates that the Ta-doped TiO2 photoanode shifts the flat band potential positively and increases the electron density. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO2. Furthermore, the increased electron density caused by the Ta-doped TiO2 improves the fill factor of the solar cell. The increased electron density accelerates the transfer rate of electrons in the Ta-doped TiO2 thin films by comparison to undoped films, which is confirmed by intensity-modulated photocurrent spectroscopy measurements.