Abstract
We report on the effect of substituting the two tetrabutyl ammonium counter ions of the standard N719 dye by sodium ions on the performance and stability of dye-sensitized solar cells (DSCs). The disodium analogue of N719 in conjunction with a non-volatile electrolyte gives a conversion efficiency of 7.6% under standard global AM 1.5 sunlight. Devices maintain 99% of their initial performance after 1000 h under full sun-light aging at 50 degrees C. Electrochemical impedance spectroscopy and photovoltage transient decay studies reveal the evolution of the solar cell parameters during aging. Remarkably, upon aging a decrease in the rate of electron back reaction with the triiodide ions across the TiO2/electrolyte interface appears as well as enhanced electronic conduction in the TiO2 film.