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

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 (V-fb) of nitrogen-doped TiO2 filth was attributed to the formation of an O-Ti-N bond, and it was indicated that the position of the edge of the V-fb 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.