Explanation of Effect of Added Water on Dye-Sensitized Nanocrystalline TiO2 Solar Cell: Correlation between Performance and Carrier Relaxation Kinetics
Time-resolved mid-IR transient absorption spectroscopy is employed to explore the mechanism of improving the performance of dye-sensitized TiO2 solar cell (DSSC) when a certain amount of H2O is added into the electrolyte. The relaxation kinetics of dye-sensitized TiO2 nanocrystalline film and the corresponding DSSC performance are investigated under different conditions. It is found that the interfacial charge recombination is retarded and electron injection efficiency is increased in the water vapour and in the electrolyte when D2O is added. The values of open-circuit photovoltage Voc and the short-circuit photocurrent Jsc of the cells are linearly correlated to the product of the two decay time constants. We also observed that Voc well correlates with electron injection efficiency. It provides a preliminary microscopic account for the function of the added water in improving the performance of DSSCs.