In nanostructured thin films, photogenerated
charge carriers can access the surface more easily than in
dense films and thus react more readily. However, the high
surface area of these films has also been associated with
enhanced recombination losses via surface states. We herein
use transient absorption spectroscopy to compare the ultrafast
charge carrier kinetics in dense and nanostructured TiO2
films for its two most widely used polymorphs: anatase and
rutile. We find that nanostructuring does not enhance recombination
rates on ultrafast timescales, indicating that
surface state mediated recombination is not a key loss pathway
for either TiO2 polymorph. Rutile shows faster, and less
intensity-dependent recombination than anatase, which we
assign to its higher doping density. For both polymorphs, we
conclude that bulk rather than surface recombination is the
primary determinant of charge carrier lifetime.