Recombination controlled signal transfer through mesoporous TiO2 films.

Photocurrent transients were used to investigate electron transport in mesoporous, nanocrystalline TiO2 films immersed into aqueous electrolyte, a regime where recombination cannot be neglected. Laser intensity and potential-dependent measurements show a decreased transient time of the current peak, which is explained by trap filling and electron loss from trap states into the electrolyte. A strongly enhanced recombination is furthermore observed, when the pH of the electrolyte is increased, while the current peak shifts toward longer transient times. Numerical simulations were used to decouple the impact of recombination and trapping on the transient response. We show that enhanced recombination in the absence of trapping accelerates the transfer of a current signal, while increased recombination slows down the transient current in the presence of electron trap sites.