In this study, we investigated the photoelectrochemical effect of guanidinium thiocyanate (GuSCN) in the base electrolyte composed of 1-methylbenzimidazole (0.45 M) and 3-methoxypropionitrile on the efficiency of electron injection (Φinj), interfacial recombination kinetics, and photovoltaic performance of dye-sensitized solar cells (DSCs). A significant increase in the photocurrent for DSCs with GuSCN was observed, which was higher than that for DSCs with the base electrolyte. The dependence of the short-circuit photocurrent density on the illumination intensity indicated that the large increase in Φinjcould be attributed to the positive shift in the flatband potential of the TiO2 electrode and could increase the electron injection yield. The results from electrochemical impedance spectroscopy (EIS) for DSCs indicated that guanidinium cation chemisorbed on the TiO2 surface could passivate the surface recombination sites and enhance the electron lifetime in the nanostructured TiO2 film to give an improved open-circuit photovoltage. The photostability of DSCs with 0.1 M GuSCN could retain over 98% of its initial photoelectric conversion efficiency value under one sun light soaking over the time of 3000 h. It is indicated that GuSCN chemisorbed on TiO2 surface could keep the interface of DSCs stable.
In this paper, the photovoltaic performance and charge recombination of the dye-sensitized solar cells (DSCs) based on nitrogen-doped TiO 2 electrodes were investigated in detail. A negative shift of the flatband potential (V fb ) of nitrogen-doped TiO 2 film 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 TiO 2 solar cells could be attributed to the formation of O-Ti-N in the TiO 2 electrode to retard the recombination reaction at the TiO 2 photoelectrode/electrolyte interface as compared to the undoped TiO 2 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 TiO 2 solar cells exhibited better stability. It indicated that the formation of O-Ti-N in the TiO 2 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 TiO 2 .
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