Retarded Charge Recombination in Dye-Sensitized Nitrogen-Doped TiO2 Solar Cells

Abstract

In this paper, the photovoltaic performance and charge recombination of the dye-sensitized solar cells (DSCs) based on nitrogen-doped TiO2 electrodes were investigated in detail. A negative shift of the flatband potential (Vfb) of nitrogen-doped TiO2 film was attributed to the formation of an O−Ti−N bond, and it was indicated that the position of the edge of the Vfb is shifted to negative, resulting in the improvement of the open circuit voltage for DSC with nitrogen doping. The UV−vis spectrum of the nitrogen-doped film exhibited a visible absorption in the wavelength range from 400 to 500 nm. The back electron transfer of the nitrogen-doped DSC was studied by measuring the electrochemistry impedance spectra (EIS), and the EIS for DSCs showed that the enhanced electron lifetime for nitrogen-doped TiO2 solar cells could be attributed to the formation of O−Ti−N in the TiO2 electrode to retard the recombination reaction at the TiO2 photoelectrode/electrolyte interface as compared to the undoped TiO2 solar cells. The photovoltaic performance of the DSC under high temperature conditions and one soaking in sun light for more than 1000 h indicated that the nitrogen-doped TiO2 solar cells exhibited better stability. It indicated that the formation of O−Ti−N in the TiO2 electrode influences the performance of the DSC. Especially, the introduction of nitrogen into the DSC can stabilize the DSC system due to the replacement of oxygen-deficient titania by nitrogen-doped TiO2.