Carrier localization and cooling in dye-sensitized nanocrystalline titanium dioxide

The transient photoconductivity of dye-sensitized titanium dioxide has been measured using time-resolved terahertz spectroscopy, a noncontact electrical probe with sub-picosecond temporal resolution. The photoconductivity deviates strongly from Drude behavior and is explained by disorder-induced carrier localization and/or backscattering of the photogenerated carriers. In addition, the carriers are found to thermally equilibrate with the lattice in roughly 300 fs. Ramifications for understanding the function of DSSCs and electrical transport in disordered media are discussed.