Quantitative study of electron losses in nanoporous anatase using transient absorption spectroscopy

To elucidate electron migration in dye-sensitized nanoporous anatase TiO2, time-of-flight short-circuit photocurrents and transient absorption spectra between 500 and 2000 nm have been recorded. It is found that electrons in TiO2 dominate the transient absorption between 900 and 1100 nm, whereas at wavelengths longer than 1100 nm absorption by electrons in the SnO2:F subst rate prevails. To facilitate a qualitative analysis, the absorption cross-s ections of electrons in TiO2 and SnO2:F have been measured. Combining trans ient absorption and photocurrent response data, the time-resolved recombina tion loss can be determined. When the excitation density is below 33.5 muJ/ cm(2), on average less than one electron per nanoparticle is injected. Unde r this condition the IPCE equals unity. When higher excitation densities ar e applied, more than one electron per nanoparticle is injected, losses beco me significant, and the IPCE reduces to 40%. The time evolution of the reco mbination loss reveals that recombination primarily takes place within a fe w microseconds.