Abstract
The effect of temperature on the charge recombination (CR) rate in bare and dye-sensitized nanocrystalline TiO2 films was studied by means of transient absorption spectroscopy. For bare TiO2 films, the CR rate was not sensitive to temperature, indicating that CR occurs by means of tunneling and without trapping of charges. By contrast, for dye-sensitized TiO2 films, the CR rate was sensitive to temperature at around room temperature, suggesting that the barrier produced by dye adsorption on the TiO2 surface had been overcome. At lower temperature, the CR rate of the dye-sensitized films was not sensitive, again suggesting a tunneling CR process. These results suggest that slow CR is not caused by charge traps but is instead caused by a barrier between a positive charge and an electron.
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