The high light-to-energy conversion efficiencies achieved with dye-sensitized solar cells (DSC) may be attributed to the nanoporous TiO₂ electrodes. Until now, the electron transport characteristic in DSC is still not clear, and it is very important to understand how electrons transport in DSC, which will help us to understand the mechanism and optimization of DSC. Intensity modulated photocurrent spectroscopy (IMPS) has been used to obtain values of the electron diffusion coefficient (Dn). Intensity-modulated photovoltage spectroscopy (IMVS) is shown to be valuable in elucidating the contributions of band edge shift and recombination kinetics.
In the present work, the electron transport characteristic was discussed by investigating the change of the absorption coefficient, electron diffusion coefficient and electron lifetime in DSC. Nanoporous films are prepared from two different sized TiO₂ nanoparticles, and DSC is prepared from these films with different thickness. The results show that the Dn increases at first, with the increase of films thickness, but Dn decrease in the range of 12 to 22 μm. Results also indicate that the electron lifetime (τn) increase with the increase of films thickness in the range of 5 to 22 μm. The increase of the Dn is interpreted with the density increase of photogenerated electrons, and then the decrease of Dn is considered as the combination in thicker films, where the more charge trap sites and grain boundary are likely to exist. The decrease of τn is discussed with the change of absorbance coefficient (α) and Dn with the films thickness.